JP4058844B2 - 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 carrier to transfer and fix a toner image formed on the image carrier onto a transfer material. The present invention relates to an electrophotographic image forming apparatus, and more particularly to an image forming apparatus capable of forming images on both sides of a transfer material.
[0002]
[Prior art]
Conventionally, in double-sided image formation, an image on one side formed on an image carrier is transferred and fixed on a transfer material, which is once stored in a double-sided reversal feeding device and formed again on the image carrier. A method is used in which a transfer material is fed from a double-sided reversal feeding device in synchronization with the transferred image, and the image on the other surface is transferred and fixed on 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 reversal feeding device and passing through the fixing device twice. It was the cause of jams and wrinkles.
[0004]
On the other hand, according to Japanese Patent Publication Nos. 49-37538, 54-28740, JP-A-1-44457, and 4-214576, etc., an image carrier and an intermediate transfer member are used to transfer a transfer material. It has been proposed to fix the toner image once after forming toner images on both sides.
[0005]
Further, the inventors of the present application have arranged a plurality of toner image forming means including charging means, image writing means, developing means, etc. around the photosensitive drum (image carrier), and formed an overlap formed on the photosensitive drum. The combined color toner image is once transferred to a belt-like intermediate transfer member in a lump, and then a color toner image is formed again on the photosensitive drum to form a toner image on the photosensitive drum and a toner image on the intermediate transfer member. The toner image on the photosensitive drum is transferred as a front image on both sides of the transfer material that is fed at the same time and conveyed by the intermediate transfer member, and the toner image on the intermediate transfer member is transferred as the back image. After that, an image forming apparatus and an image forming method for separating a transfer material from an intermediate transfer member and fixing a toner image on the transfer material to form a double-sided color image are disclosed in JP-A-9-258492 and JP-A-9-25. Disclosed in 516 JP.
[0006]
[Problems to be solved by the invention]
In a double-sided image forming apparatus that forms an image on both sides of a transfer material using a belt-like intermediate transfer member as described above, primary transfer that transfers the toner image on the image carrier onto the surface of the transfer material or to the intermediate transfer member. And a secondary transfer means for transferring the toner image on the intermediate transfer member to the back surface of the transfer material. When forming a double-sided image, the toner image (back surface) on the image carrier is temporarily transferred by the primary transfer means. Transfer to the intermediate transfer member, and then the toner image (surface) on the formed image carrier is transferred to the surface of the transfer material by the primary transfer means, and then the toner image (surface) is held on the surface of the transfer material The material is charged from above by secondary transfer means to transfer the toner image (back surface) on the intermediate transfer member to the back surface of the transfer material, and double-sided image formation is performed in which the toner image is held on both surfaces of the transfer material. On the other hand, at the time of surface (single-sided) image formation, the toner image (surface) on the image carrier is transferred to the surface of the transfer material by primary transfer means, and surface (single-sided) image formation is performed.
[0007]
The transfer material holding the toner image on both sides or the surface (single side) is nipped and fixed by two fixing members (fixing rollers) in a heated state, and good fixing is achieved in any of them. In many cases, the toner image is disturbed. The present inventors have investigated the reason why the toner image is disturbed at the time of fixing, and carried out the present invention. For the transfer material holding the toner image on both surfaces, the transfer material holding the toner image on the surface is also used. However, it is an object of the present invention to provide an image forming apparatus in which the toner image is not disturbed at the time of fixing.
[0008]
[Means for Solving the Problems]
The above purpose is
An image carrier, a means for forming a toner image on the image carrier, an endless belt-shaped intermediate transfer member which can carry the toner image and supports and conveys a transfer material, and a toner image on the image carrier Is transferred to the surface of the transfer material or the intermediate transfer member, the secondary transfer unit is configured to transfer the toner image on the intermediate transfer member to the back surface of the transfer material, and the toner image is carried on both the front and back surfaces. And a fixing unit that fixes the transferred material between the fixing members. When forming a double-sided image, the secondary transfer unit applies the transfer material onto the transfer material. Surface toner image It has a charging step for transferring the back surface toner image from above, and has a charging step similar to the above transfer for reversing the toner polarity on the transfer material from above the toner image on the transfer material at the time of surface image formation, After that, it is configured to perform static elimination and fixing, and the electric field condition applied between the fixing members during double-sided image formation is the same as the electric field condition applied between the fixing members during surface image formation. The electric field formed between the fixing members that sandwich and fix the transfer material of the fixing unit is an electric field in a direction that attracts toner to the transfer material. Ruko An image forming apparatus characterized by the above (Invention of Claim 1)
Is achieved.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Prior to the description of the embodiments of the present invention, an image forming apparatus capable of common double-sided image formation and single-sided image formation will be described first. The description in this column does not limit the technical scope of the claims or the meaning of 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. In the following description of the embodiments, the surface of the transfer material facing the image carrier in the transfer area is referred to as the front surface, and the other surface of the transfer material, that is, the surface of the transfer material facing the intermediate transfer member is referred to as the back surface. An image transferred onto the surface of the transfer material is referred to as a front image, and an image transferred onto the back surface of the transfer material is referred to as a back image.
[0010]
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 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 cross-sectional view of the image carrier of FIG. 1, and FIG. FIG. 3A is a diagram illustrating a toner image formation state on both surfaces of a transfer material in an image forming apparatus according to the invention, and FIG. 3A is a toner image when a back image formed on an image carrier is transferred onto an intermediate transfer member; FIG. 3B is a diagram illustrating a toner image formation state when a front surface image is formed on the image carrier in synchronization with the back surface image on the intermediate transfer member. FIG. 4C is a diagram illustrating double-sided image formation on the transfer material, and FIG. 4 is a diagram illustrating a toner image formation state on the surface (one side) of the transfer material.
[0011]
In FIG. 1, 10 is a photosensitive drum as an image carrier, 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, an intermediate transfer belt as an intermediate transfer member, 14c, means for transferring a toner image on the image carrier to the intermediate transfer member, and means for transferring the toner image on the image carrier to the surface of the transfer material. 14g is a secondary transfer unit that is a means for transferring the toner image on the intermediate transfer member to the back surface of the transfer material, 14m is a charge removal unit that is a charge removal means, and 150 is a paper that is a transfer material charging means. Reference numeral 14h denotes a paper separation AC static eliminator serving as a transfer material separating unit, 160 denotes a conveying unit having a separation claw 210 serving as a claw member and a spur 162 serving as a spur member, and 17 denotes a fixing device serving as a fixing unit.
[0012]
A photosensitive drum 10 as an image carrier is formed on the outer periphery of a cylindrical substrate formed of a transparent member such as optical glass or transparent acrylic resin, for example, on a transparent conductive layer, an a-Si layer, or an organic photosensitive layer (OPC). ) And the like, and is rotated in the clockwise direction indicated by the arrow in FIG. 1 at a linear velocity of, for example, 80 to 400 mm / sec with the conductive layer grounded.
[0013]
As shown in FIG. 2, the photosensitive drum 10 is fixed to a drum shaft 30 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 supported by the bearing and rotatably supported, and is integrated with the flange member 10B is engaged with a drive gear (not shown) on the apparatus main body side and driven to rotate in a predetermined direction at a constant speed.
[0014]
A means for forming a toner image on the image carrier comprises a scorotron charger 11 as a charging means, an exposure optical system 12 as an image writing means, and a developing device 13 as a developing means. Four sets are provided for the image forming process of each color of (Y), magenta (M), cyan (C), and black (K), and the rotation direction of the photosensitive drum 10 indicated by the arrow in FIG. , M, C, K.
[0015]
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.
[0016]
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 includes a plurality of LEDs (light emitting diodes) as light emitting elements for image exposure light (image writing light) arranged in parallel to the drum shaft 30 in the main scanning direction. An exposure unit composed of linear exposure elements 12a arranged in an array, a light converging light transmitter (trade name: Selfoc lens array) 12b as an imaging element, and a lens holder 12c. It 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 in the translucent substrate of the photosensitive drum 10. The exposure optical system 12 for each color writes an image on 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 is statically applied on the photosensitive drum 10. An electrostatic 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 in addition to the LED. The light emitting wavelength of the light emitting element for image exposure light (image writing light) is usually in the range of 780 to 900 nm, which is highly transmissive to Y, M, and C toners. Therefore, a shorter wavelength of 400 to 780 nm which does not have sufficient transparency to the color toner may be used. Since 80% or more of the image exposure light is absorbed by the photosensitive layer of the photosensitive drum 10, the influence of reflection and absorption by the color toner on the surface of the photosensitive drum 10 can be ignored. In general, the order of developing color toners is preferably Y, M, C, and K in order of the color mixture of the toner image and the developing device 13. In FIG. 2, WA is a lead wire from a light emitting element (LED) for image exposure light.
[0017]
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. Inside the developing casing 138, yellow (Y), magenta (M), Contains one-component or two-component developer of cyan (C) and black (K). 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.
[0018]
The intermediate transfer belt 14a, which is an intermediate transfer body, has a volume resistivity of 10 ⁸ -10 ¹² An endless belt of Ω · cm, for example, a thickness of 0.1 to 1.0 mm in which a conductive material is dispersed in engineering plastics such as modified polyimide, thermosetting polyimide, ethylene tetrafluoroethylene copolymer, polyvinylidene fluoride, nylon alloy, etc. A seamless belt having a two-layer structure in which a fluorine coating having a thickness of 5 to 50 μm is preferably provided on the outer side of the semiconductive film substrate as a toner filming prevention layer. As the base of the intermediate transfer belt 14a, a semiconductive rubber belt having a thickness of 0.5 to 2.0 mm in which a conductive material is dispersed in silicon rubber or urethane rubber can also be used. The intermediate transfer belt 14a is stretched around a driving roller 14d, a ground roller 14j, a driven roller 14e, a guide roller 14f, and a tension roller 14i, which are roller members, and is rotated counterclockwise as indicated by an arrow in FIG. The guide roller 14f, the driven roller 14e, the earth roller 14j, and the driving roller 14d are fixed and rotated, and the tension roller 14i is supported and rotated so as to be movable by an elastic force such as a spring (not shown). The drive roller 14d is rotated by driving from a drive motor (not shown), and the intermediate transfer belt 14a is driven to rotate. The ground roller 14j, the driven roller 14e, the guide roller 14f, and the tension roller 14i are driven and rotated by the rotation of the intermediate transfer belt 14a. The slack of the rotating intermediate transfer belt 14a is tensioned by the tension roller 14i. The recording paper P, which is a transfer material, is supplied to a position where the intermediate transfer belt 14a is stretched around the driven roller 14e, and is conveyed by the intermediate transfer belt 14a. The recording paper P is separated from the intermediate transfer belt 14a at the curvature portion KT at the end of the intermediate transfer belt 14a stretched around the drive roller 14d on the fixing device 17 side.
[0019]
A primary transfer unit 14c as a means for transferring the toner image on the image carrier to the intermediate transfer member and a means for transferring the toner image on the image carrier to the surface of the transfer material is a photosensitive member with the intermediate transfer belt 14a interposed therebetween. It is a corona discharge device provided opposite to the drum 10, and forms a transfer area 14 b between the intermediate transfer belt 14 a and the photosensitive drum 10. A DC voltage having a polarity opposite to that of the toner (plus polarity in this embodiment) is applied to the primary transfer device 14c, and the toner image on the photosensitive drum 10 is transferred onto the intermediate transfer belt 14a or the recording paper P as a transfer material. Transfer to the surface.
[0020]
The secondary transfer unit 14g, which is a secondary transfer unit that transfers the toner image on the intermediate transfer member to the back surface of the transfer material, is preferably constituted by a corona discharger and is driven with the primary transfer unit 14c with the intermediate transfer belt 14a interposed therebetween. A DC voltage having a polarity opposite to that of the toner (positive polarity in the present embodiment) is applied to the earth roller 14j provided between the roller 14d and the toner image on the intermediate transfer belt 14a. Transfer to the back of the.
[0021]
The static eliminator 14m serving as a static eliminator is constituted by a corona discharger, and is provided in parallel with the primary transfer unit 14c on the downstream side of the primary transfer unit 14c with respect to the moving direction of the intermediate transfer belt 14a. The charge of the intermediate transfer belt 14a, which is applied and charged by the voltage application of the primary transfer unit 14c, is removed.
[0022]
The paper charger 150 serving as a transfer material charging unit is preferably formed of a sawtooth electrode, and is provided to face the driven roller 14e that is grounded with the intermediate transfer belt 14a interposed therebetween, and has the same polarity as the toner (in this embodiment, A negative polarity) DC voltage is applied to charge the recording paper P and attract it to the intermediate transfer belt 14a. As the paper charger 150, in addition to the sawtooth electrode, a corona discharger, a paper charging brush or a paper charging roller capable of coming into contact with and releasing from the intermediate transfer belt 14a can be used.
[0023]
The paper separating AC static eliminator 14h, which is a transfer material separating means, is preferably constituted by a corona discharger, and is opposed to a driving roller 14d that is grounded with the intermediate transfer belt 14a sandwiched between ends of the intermediate transfer belt 14a on the fixing device 17 side. As will be described later, an AC voltage superimposed with a DC voltage having the same polarity as the DC voltage applied to the secondary transfer device 14g (plus polarity in this embodiment) is applied and conveyed by the intermediate transfer belt 14a. The recording paper P to be discharged is discharged and separated from the intermediate transfer belt 14a.
[0024]
The transport unit 160 includes a separation claw 210 that is a claw member and a spur 162 that is a spur member, and is provided between the curvature portion KT at the end of the intermediate transfer belt 14 a on the fixing device 17 side and the fixing device 17. The transport unit 160 may cause the intermediate transfer belt 14a to be deformed by heat from the fixing device 17, or the toner image carried on the intermediate transfer belt 14a may become fused and difficult to transfer, or may be on the intermediate transfer belt 14a. The toner is prevented from adhering to the toner.
[0025]
The separation claw 210 as a claw member is provided close to the curvature portion KT of the intermediate transfer belt 14a and fixed to the support shaft 221 with a predetermined distance, preferably 0.1 to 2.0 mm, from the intermediate transfer belt 14a. When the recording paper P is separated from the intermediate transfer belt 14a, the leading edge of the recording paper P that is to be bent and conveyed in the direction of the intermediate transfer belt 14a is brought into contact with the recording paper P to assist the separation of the recording paper P.
[0026]
The spur 162, which is a spur member, has a plurality of protrusions 162a on the peripheral surface, and is provided so as to be rotatable about the rotation support shaft 165. The spur 162 guides the back side of the recording paper P and conveys the recording paper P to prevent the back side toner image of the recording paper P having a toner image on both sides from being disturbed and to fix the recording paper P to the fixing device 17. The recording paper P is stably conveyed to the fixing device 17 while keeping the entering direction constant.
[0027]
The separation claw 210 and the spur 162 are disposed on the opposite side of the photosensitive drum 10 with respect to the transfer material conveying surface on the intermediate transfer belt 14a or its extended surface. It is also possible to provide a spur 162 as a spur member on both sides of the transfer material conveying surface or its extended surface.
[0028]
The fixing device 17 serving as a fixing unit includes two roller-shaped fixing members including a first fixing roller 17a and a second fixing roller 17b each having a heater therein, and the first fixing roller 17a and the second fixing roller 17b. The recording paper P is nipped and conveyed at the nip portion T between the two and the toner image on the recording paper P conveyed through the nip portion T is fixed by adding heat and pressure. Each of the first fixing roller 17a and the second fixing roller 17b is provided with high resistance layers 173a and 173b, which will be described in detail later, as surface layers, and a bias voltage, which will be described in detail later, is applied.
[0029]
Next, the image forming process will be described. First, the double-sided image forming process will be described.
[0030]
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.
[0031]
After the photosensitive drum 10 is applied with an electric potential, the Y exposure optical system 12 starts image writing with an electrical signal corresponding to the first color signal, that is, the Y image data for the back image, and the photosensitive drum 10. An electrostatic latent image corresponding to the Y image of the original image is formed on the surface of the image.
[0032]
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.
[0033]
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. .
[0034]
By a similar process, a cyan (C) toner image corresponding to the third color signal is further superimposed by a cyan (C) scorotron charger 11, a C exposure optical system 12, and a C developer 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, within one rotation of the photosensitive drum 10, a superimposed color toner image of four colors of yellow (Y), magenta (M), cyan (C) and black (K) is formed on the peripheral surface.
[0035]
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 translucent substrate. Therefore, writing of images corresponding to the second, third, and fourth color signals is performed without any influence from the previously formed toner image, and is equivalent to the image corresponding to the first color signal. It is possible to form an electrostatic latent image.
[0036]
The superimposed color toner image, which is the back image formed on the photosensitive drum 10 as the image carrier by the above image forming process, is transferred to the intermediate transfer member as an intermediate transfer member by the primary transfer unit 14c in the transfer region 14b. The images are collectively transferred onto the belt 14a (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. Further, the charge on the intermediate transfer belt 14a charged by the primary transfer device 14c is discharged by the charge eliminator 14m.
[0037]
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 which is an image carrier cleaning means or abuts against the photosensitive drum 10. It is cleaned by the cleaning blade 19a made of the rubber material and collected in a waste toner container (not shown) by the screw 19b. 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.
[0038]
After the superimposed color toner image to be the back image is formed on the intermediate transfer belt 14a as described above, it is continuously superimposed on the surface of the photosensitive drum 10 in the same manner as the color image forming process described above. A combined color toner image is formed (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.
[0039]
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 feeding means. By driving the timing roller 15b, the color toner image of the front image formed on the photosensitive drum 10 and the color toner image of the back image carried on the intermediate transfer belt 14a are synchronized. It is fed to the transfer area 14b. At this time, the fed recording paper P is charged to the same polarity as the toner by a paper charger 150 which is a transfer material charging means provided on the surface side of the recording paper P, and is attracted to the intermediate transfer belt 14a to be transferred 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 intermediate transfer belt 14a or the toner image on the photosensitive drum 10, thereby preventing the toner image from being disturbed.
[0040]
In the transfer area 14b, the surface image on the photosensitive drum 10 is collectively transferred onto the surface of the recording paper P by the primary transfer device 14c to which a voltage having a polarity opposite to that of the toner (plus polarity in the present embodiment) is applied. . At this time, the back image on the intermediate transfer belt 14a is not transferred to the recording paper P and exists on the intermediate transfer belt 14a. At this time, uniform exposure is performed by a transfer simultaneous exposure device 12d using, for example, a light-emitting diode, which is provided inside the photosensitive drum 10 so as to face the transfer region 14b so as to achieve good transfer. May be. Further, the charge on the intermediate transfer belt 14a charged by the primary transfer device 14c is discharged by the charge eliminator 14m.
[0041]
The recording paper P on which the color toner image has been transferred is conveyed to a secondary transfer device 14g to which a voltage having a polarity opposite to that of the toner (positive polarity in the present embodiment) is applied, and is intermediately transferred by the secondary transfer device 14g. The back image on the peripheral surface of the transfer belt 14a is transferred to the back surface of the recording paper P at once (FIG. 3C).
[0042]
The recording paper P on which the color toner images are formed on both sides is neutralized by the curvature of the curvature portion KT of the intermediate transfer belt 14a and the paper separation AC static eliminator 14h as a transfer material separation means provided at the end of the intermediate transfer belt 14a. The fixing device as a fixing means is separated from the intermediate transfer belt 14 a by the action and the separation claw 210 provided in the conveyance unit 160 with a predetermined distance from the intermediate transfer belt 14 a and through a spur 162 provided in the conveyance unit 160. 17, and is conveyed between the nip portion T between the first fixing roller 17 a and the second fixing roller 17 b, and heat and pressure are added in the nip portion T, whereby the toner image on the recording paper P is formed. It is fixed. The recording paper P on which double-sided image recording has been performed is sent with its front and back reversed and discharged by a paper discharge roller 18 to a tray outside the apparatus.
[0043]
The toner remaining on the peripheral surface of the intermediate transfer belt 14a after the transfer is provided so as to face the guide roller 14f with the intermediate transfer belt 14a interposed therebetween, and abuts against and contacts the intermediate transfer belt 14a with the support shaft 142 as a rotation fulcrum. Cleaning is performed by an intermediate transfer body cleaning device 140 that is an intermediate transfer body cleaning unit having an intermediate transfer body cleaning blade 141 that can be contacted and released.
[0044]
The toner remaining on the peripheral surface of the photosensitive drum 10 after the transfer is discharged by the photosensitive drum AC static eliminator 16 and then cleaned by the cleaning device 19, and is further cleaned by the uniform exposure unit 12e before charging. The history of the photoconductive drum 10 in the image formation is canceled, 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 intermediate transfer belt 14a, toner scattering and rubbing are unlikely to occur, and good double-sided color image with little image deterioration Formation is made.
[0046]
Next, a front surface (single side) image forming process will be described.
[0047]
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.
[0048]
After the photosensitive drum 10 is applied with a potential, the Y exposure optical system 12 starts image writing with the first color signal for the surface image, that is, the electrical signal corresponding to the Y image data. An electrostatic latent image corresponding to the Y image of the original image is formed on the surface of the image.
[0049]
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.
[0050]
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. .
[0051]
By a similar process, a cyan (C) toner image corresponding to the third color signal is further superimposed by a cyan (C) scorotron charger 11, a C exposure optical system 12, and a C developer 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, within one rotation of the photosensitive drum 10, four color toner images of yellow (Y), magenta (M), cyan (C) and black (K) are formed on the peripheral surface (FIG. 4). (A)).
[0052]
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 translucent substrate. Therefore, writing of images corresponding to the second, third, and fourth color signals is performed without any influence from the previously formed toner image, and is equivalent to the image corresponding to the first color signal. It is possible to form an electrostatic latent image.
[0053]
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 feeding means. And is fed to the transfer area 14b in synchronism with the color toner image of the surface image formed on the photosensitive drum 10 by the driving of the timing roller 15b. At this time, the fed recording paper P is charged to the same polarity as the toner by a paper charger 150 which is a transfer material charging means provided on the surface side of the recording paper P, and is attracted to the intermediate transfer belt 14a to be transferred 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 intermediate transfer belt 14a or the toner image on the photosensitive drum 10, thereby preventing the toner image from being disturbed.
[0054]
In the transfer area 14b, the surface image on the photosensitive drum 10 is collectively transferred onto the surface of the recording paper P by the primary transfer device 14c to which a voltage having a polarity opposite to that of the toner (plus polarity in the present embodiment) is applied. . At this time, uniform exposure is performed by a transfer simultaneous exposure device 12d using, for example, a light-emitting diode, which is provided inside the photosensitive drum 10 so as to face the transfer region 14b so as to achieve good transfer. May be. The charge on the intermediate transfer belt 14a charged by the primary transfer unit 14c is discharged by the charge eliminator 14m (FIG. 4B).
[0055]
The recording paper P having a color toner image formed on the surface thereof is neutralized by the curvature of the curvature portion KT of the intermediate transfer belt 14a and the paper separation AC static eliminator 14h as a transfer material separation means provided at the end of the intermediate transfer belt 14a. The fixing device as a fixing means is separated from the intermediate transfer belt 14 a by the action and the separation claw 210 provided in the conveyance unit 160 with a predetermined distance from the intermediate transfer belt 14 a and through a spur 162 provided in the conveyance unit 160. 17, and is conveyed between the nip portion T between the first fixing roller 17 a and the second fixing roller 17 b, and heat and pressure are added in the nip portion T, whereby the toner image on the recording paper P is formed. It is fixed. The recording paper P on which the front surface image has been recorded is fed with its front and back reversed, and is discharged by a paper discharge roller 18 to a tray outside the apparatus.
[0056]
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 cleaned by the cleaning device 19, and the previous image is obtained by the uniform exposure unit 12e before charging. The history of the photosensitive drum 10 in the formation is eliminated, and the next image forming cycle is started.
[0057]
A first fixing roller 17a and a second fixing roller which are two roll-shaped fixing members provided in the fixing device 17 which is a fixing means used in the above-described double-sided or front-side (single-sided image forming) image forming apparatus. As shown in FIG. 5 or 7, the structure 17 b fixes the first fixing roller 17 a for fixing the upper (front side) toner image on the recording paper P and the lower (back side) toner image. For this purpose, the second fixing roller 17b is a rotating body having substantially the same structure in which halogen heaters HL1 and HL2 are provided at the inner centers. The first fixing roller 17a having the halogen heater HL1 at the center has a cylindrical metal pipe 171a using, for example, an aluminum material, and a volume of 1 to 3 mm using, for example, a silicon material on the outer peripheral surface of the metal pipe 171a. Resistivity is 10 ^Four -10 ^Ten A rubber roller layer 172a made of a thin rubber layer having a low or medium resistance of Ω · cm, and a surface resistivity of the rubber roller layer 172a with a layer thickness (thickness) of 0.05 to 0.25 mm and a volume resistivity of the intermediate transfer described above. The volume resistivity of the belt 14a (10 ⁸ -10 ¹² Ω · cm) or volume resistivity of the recording paper P as a transfer material (approximately the same as the intermediate transfer belt 14a) ⁸ -10 ¹² 10 higher than Ω · cm) ¹⁴ It is configured as a soft roller on which a high resistance layer 173a having heat resistance and releasability, such as fluororesin such as PFA and PTFE of Ω · cm or more, and silicon resin is formed. Similarly, the second fixing roller 17b having the halogen heater HL2 in the central portion has a cylindrical metal pipe 171b using, for example, an aluminum material, and a thickness of 1 to 10 mm using, for example, a silicon material on the outer peripheral surface of the metal pipe 171b. And the volume resistivity is 10 ^Four -10 ^Ten A rubber roller layer 172b made of a low or medium resistance rubber layer of Ω · cm, and a layer resistivity (thickness) of 0.02 to 0.20 mm and a volume resistivity of 10 on the surface of the rubber roller layer 172b. ¹⁴ It is configured as a soft roller on which a high resistance layer 173b having heat resistance and releasability such as fluororesin such as PFA and PTFE of not less than Ω · cm and silicon resin is formed. By providing high resistance layers 173a and 173b having a higher volume resistivity than the recording paper P and the intermediate transfer belt 14a on the fixing member of the fixing device 17, the resistance of the fixing member is low, or the fixing member is grounded. In this case, charge leakage from the recording paper P and the intermediate transfer belt 14a through the fixing member is prevented, and fixing is performed when the back surface toner image is transferred by the secondary transfer device 14g disposed near the fixing device 17. This prevents the back surface toner image from being transferred favorably due to charge leakage from the recording paper P through the member.
[0058]
FIG. 5 shows the state of charge when forming a double-sided image. A color toner image (negative polarity in the present embodiment) of the surface image formed on the photosensitive drum 10 by the recording paper P as a transfer material is shown. The color toner image of the back surface image carried on the intermediate transfer belt 14a (synchronous with the negative polarity in this embodiment) is synchronized and fed to the transfer area 14b, and in the transfer area 14b, the opposite polarity to the toner ( In this embodiment, the surface image on the photosensitive drum 10 is transferred onto the surface of the recording paper P by the primary transfer device 14c to which a DC voltage having a positive polarity is applied. At this time, the intermediate transfer belt 14a (volume resistivity is 10 ⁸ -10 ¹² Since the surface toner image on the recording paper P is transferred across (Ω · cm), the surface toner image on the recording paper P is kept in the negative polarity without being converted in polarity. Further, after the charge of the intermediate transfer belt 14a charged to the positive polarity by the primary transfer device 14c is discharged by the charge remover 14m to which an AC voltage is applied, the back surface toner image on the intermediate transfer belt 14a is opposite to the toner. The image is transferred to the back surface of the recording paper P by the secondary transfer device 14g to which a DC voltage having a polarity (positive polarity in the present embodiment) is applied. The circle (a) in FIG. 5 after passing through the secondary transfer device 14g. As shown in FIG. 6, the charge state between the front and back toner images and the recording paper P at the position is maintained in the negative polarity without changing the polarity of the back toner image on the recording paper P. The upper surface toner image having a negative polarity is converted into a positive polarity by a positive polarity discharge by the secondary transfer unit 14g. Further, the surface side of the recording paper P is also positively charged by the positive polarity discharge by the secondary transfer device 14g, and the volume resistivity of the recording paper P is low, so that the positive charge is in the center or the back side (back side) of the recording paper P. It is also turning around. At this time, the potential of the recording paper P is charged to 1 to 2 kV with a positive polarity on the secondary transfer counter roller 14j across the intermediate transfer belt 14a.
[0059]
The recording paper P on which the color toner images are formed on both sides is the same as the curvature of the curvature portion KT of the intermediate transfer belt 14a and the DC voltage applied to the end of the intermediate transfer belt 14a and applied to the secondary transfer device 14g. AC voltage V superimposed with DC voltage plus 500V of polarity (plus polarity in this embodiment as described above in FIG. 6). _pp The sheet is separated from the intermediate transfer belt 14a by the sheet removing AC neutralizer 14h as a transfer material separating unit to which 10 kV and 1 kHz are applied, and the separation claw 210, and is fixed as a fixing unit through a spur 162 which is a spur member. The sheet is conveyed to the apparatus 17, conveyed between the nip portions T between the first fixing roller 17 a and the second fixing roller 17 b, and a loop is formed on the recording paper P while being nipped by the nip portion T, and the nip The toner image on the recording paper P is fixed by adding heat and pressure at the portion T. However, the secondary transfer counter roller 14j by the secondary transfer device 14g described above is removed by the charge removing action of the paper separating AC charge remover 14h. The potential of the recording paper P having a positive polarity of 1 to 2 kV is neutralized to about 200 to 700 V with a positive polarity on the driving roller 14d across the intermediate transfer belt 14a. .
[0060]
FIG. 7 shows the state of charge during the formation of the front surface (single side) image. The color toner image of the front surface image formed on the photosensitive drum 10 by the recording paper P as a transfer material (minus in this embodiment). The photosensitive drum is fed by a primary transfer device 14c to which a DC voltage having a polarity opposite to that of the toner (positive polarity in the present embodiment) is applied in the transfer zone 14b. The surface image on 10 is collectively transferred to the surface of the recording paper P. At this time, the intermediate transfer belt 14a (volume resistivity is 10 ⁸ -10 ¹² Since the surface toner image on the recording paper P is transferred across (Ω · cm), the polarity of the surface toner image on the recording paper P is not changed and is kept negative. Further, the charge of the intermediate transfer belt 14a charged to the positive polarity by the primary transfer device 14c is discharged by the charge remover 14m to which the AC voltage is applied.
[0061]
The recording paper P having a color toner image formed on the surface is provided at the curvature of the curvature portion KT of the intermediate transfer belt 14a and the end of the intermediate transfer belt 14a, and has the same polarity as the surface toner image (as shown in FIG. 8). In this embodiment, an AC voltage V is superimposed with a negative polarity (DC voltage minus 500 V). _pp The sheet is separated from the intermediate transfer belt 14a by the sheet removing AC neutralizer 14h as a transfer material separating unit to which 10 kV and 1 kHz are applied, and the separation claw 210, and is fixed as a fixing unit through a spur 162 which is a spur member. The sheet is conveyed to the apparatus 17, conveyed between the nip portions T between the first fixing roller 17 a and the second fixing roller 17 b, and a loop is formed on the recording paper P while being nipped by the nip portion T, and the nip The toner image on the recording paper P is fixed by adding heat and pressure at the part T, but the secondary transfer counter roller 14j is sandwiched between the intermediate transfer belt 14a by the static elimination action of the paper separation AC static eliminator 14h. Then, the potential of the recording paper P having a negative polarity of 1 to 2 kV is neutralized to about 200 to 700 V with a negative polarity on the driving roller 14d across the intermediate transfer belt 14a. That.
[0062]
( Reference form )
As described above, the recording paper P on which double-sided image formation has been performed is an AC voltage (for example, Vp-p10 kV) in which a DC voltage (for example, plus 500 V) having a reverse polarity (plus polarity) is superimposed on the toner used by the paper separation AC static eliminator 14h. , 1 kHz) to be separated from the intermediate transfer belt 14a, and the recording paper P is conveyed to the fixing device 17 in the state of toner charge as shown in FIG. The toner and the recording paper P are positively charged at 200 to 700 V on the driving roller 14d.
[0063]
The recording paper P on which the front surface (one side) image is formed has an alternating voltage (for example, Vp−p10 kV, for example) superimposed with a direct current voltage (for example, negative 500 V) of the same polarity (negative polarity) as that of the toner used by the paper separation AC static eliminator 14h. 1 kHz) is separated from the applied intermediate transfer belt 14a, and the recording paper P is conveyed to the fixing device 17 in the state of toner charge as shown in FIG. The recording paper P is negatively charged at −200 to −700 V on the driving roller 14d.
[0064]
Book Reference form The electric field formed between the first fixing roller 17a and the second fixing roller 17b, which are fixing members of the fixing device 17, is changed in reverse between the double-sided image formation and the front surface (single-sided) image formation, In any case, the toner is prevented from being disturbed as an electric field that presses the toner adhering to the paper side. FIG. 9 shows a bias condition between the fixing rollers, and FIG. FIG. 9B shows the bias conditions for fixing the recording paper P with the front (single side) image.
[0065]
At the time of double-sided image formation, a positive voltage V1a is applied to the metal pipe 171a via the protective resistance for the first fixing roller 17a facing the surface of the recording paper, and via the protective resistance for the second fixing roller 17b. Then, a negative voltage V1b is applied to the metal pipe 171b, and an electric field of 200 V to 2 kV is formed in the direction indicated by the arrow EF1 as a potential difference. Thus, any toner on the recording paper P acts to be pressed in the paper direction, and the toner image is prevented from being disturbed during fixing.
[0066]
Further, when forming a front (single side) image, a negative voltage V2a is applied to the metal pipe 171a via the protective resistance for the first fixing roller 17a, and a positive voltage is applied to the second fixing roller 17b via the protective resistance. The voltage V2b is applied to the metal pipe 171b. In this case, the positive voltage V2b applied to the second fixing roller 17b may be omitted. By applying such a voltage, an electric field in the direction of arrow EF2 is formed between the fixing members by a potential difference of 200 V to 2 kV. As a result, the negatively charged toner adhering to the surface of the recording paper P acts to be pulled toward the paper side, and the toner image is prevented from being disturbed during fixing.
[0067]
Here, since any voltage applied to the fixing roller is applied to the metal pipe that is the core metal, the applied voltage is that the rubber roller layers 172a and 172b that are elastic layers are insulative or conductive. Depends on the volume resistivity of 10 ^Four -10 ^Ten When the resistance is low or medium resistance of Ω · cm, the applied voltage may be as low as 200 V to 2 kV. The voltage applied to the upper and lower rollers is relative as long as the electric field to be formed is formed as described above, and one of the voltages may be grounded or applied to both.
[0068]
The switching of the electric field formed between the fixing members described above is performed as follows. That is, the control unit of the image forming apparatus (not shown) determines whether the next image to be formed is a double-sided image or a single-sided image according to the double-sided image forming program or the single-sided image forming program stored in the memory. However, as a part of the double-sided image forming program, an applied voltage to be applied to the fixing member at the time of fixing the double-sided image is incorporated, and as a part of the single-sided image forming program, an applied voltage to be applied to the fixing member at the time of single-sided image fixing is As a result of the incorporation, a good image free of toner image distortion can be obtained for both images on both sides.
[0069]
( Embodiment )
Claim 1-2 Invention
About double-sided image formation Reference form Since it is formed and fixed in exactly the same manner as described in FIG. For surface (single-sided) image formation, a transfer bias at the time of double-sided image formation is applied from above a transfer material holding a toner image on the surface using a secondary transfer means that has not been used conventionally. As a result, the electric field condition between the fixing members suitable for fixing the transfer material holding the double-sided image is used as it is for fixing the transfer material holding the surface (single-sided) image, and the toner image is satisfactorily fixed without distortion. Will be. Next, a front surface (single side) image forming process in the present embodiment will be described.
[0070]
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.
[0071]
After the photosensitive drum 10 is applied with a potential, the Y exposure optical system 12 starts image writing with the first color signal for the surface image, that is, the electrical signal corresponding to the Y image data. An electrostatic latent image corresponding to the Y image of the original image is formed on the surface of the image.
[0072]
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.
[0073]
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. .
[0074]
By a similar process, a cyan (C) toner image corresponding to the third color signal is further superimposed by a cyan (C) scorotron charger 11, a C exposure optical system 12, and a C developer 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, within one rotation of the photosensitive drum 10, a superimposed color toner image of four colors of yellow (Y), magenta (M), cyan (C) and black (K) is formed on the peripheral surface.
[0075]
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 feeding means. And is fed to the transfer area 14b in synchronism with the color toner image of the surface image formed on the photosensitive drum 10 by the driving of the timing roller 15b. At this time, the fed recording paper P is charged to the same polarity as the toner by a paper charger 150 which is a transfer material charging means provided on the surface side of the recording paper P, and is attracted to the intermediate transfer belt 14a to be transferred 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 intermediate transfer belt 14a or the toner image on the photosensitive drum 10, thereby preventing the toner image from being disturbed.
[0076]
In the transfer area 14b, the surface image on the photosensitive drum 10 is collectively transferred onto the surface of the recording paper P by the primary transfer device 14c to which a voltage having a polarity opposite to that of the toner (plus polarity in the present embodiment) is applied. . At this time, uniform exposure is performed by a transfer simultaneous exposure device 12d using, for example, a light-emitting diode, which is provided inside the photosensitive drum 10 so as to face the transfer region 14b so as to achieve good transfer. May be. Further, the charge on the intermediate transfer belt 14a charged by the primary transfer device 14c is discharged by the charge eliminator 14m.
[0077]
The recording paper P having the color toner image transferred on the surface is conveyed to a secondary transfer device 14g to which a voltage having a polarity opposite to that of the toner (positive polarity in this embodiment) is applied, and is recorded by the secondary transfer device 14g. The same charging is performed from the top of the toner image on the paper P as in the back side image transfer.
[0078]
The recording paper P having a color toner image formed on the surface is double-sided by the curvature of the curvature portion KT of the intermediate transfer belt 14a and the paper separation AC static eliminator 14h as a transfer material separation means provided at the end of the intermediate transfer belt 14a. The spurs separated from the intermediate transfer belt 14a and provided on the transport unit 160 by the charge eliminating action under the same conditions as in image formation and the separation claw 210 provided on the transport unit 160 with a predetermined distance from the intermediate transfer belt 14a. 162 is conveyed to a fixing device 17 serving as a fixing unit, and is conveyed between the nip portion T between the first fixing roller 17a and the second fixing roller 17b. At the nip portion T, heat, pressure, and double-sided image formation are performed. By adding the same electric field condition, the toner image on the recording paper P is fixed. The recording paper P on which double-sided image recording has been performed is sent with its front and back reversed and discharged by a paper discharge roller 18 to a tray outside the apparatus.
[0079]
FIG. 10 shows the state of charge during surface (single-sided) image formation in this embodiment, and a color toner image (this embodiment) of the surface image on which the recording paper P as a transfer material is formed on the photosensitive drum 10. Primary transfer device 14c to which a DC voltage having a polarity opposite to that of the toner (in this embodiment, a positive polarity) is applied in the transfer region 14b. As a result, the surface images on the photosensitive drum 10 are collectively transferred onto the surface of the recording paper P. At this time, the intermediate transfer belt 14a (volume resistivity is 10 ⁸ -10 ¹² Since the surface toner image on the recording paper P is transferred across (Ω · cm), the surface toner image on the recording paper P is kept in the negative polarity without being converted in polarity. Further, the charge of the intermediate transfer belt 14a charged to the positive polarity by the primary transfer device 14c is discharged by the charge remover 14m to which the AC voltage is applied. The negative transfer surface toner image on the recording paper P is converted into a secondary image by the secondary transfer device 14g to which a DC voltage of the same condition is applied when forming a double-sided image having a polarity opposite to that of the toner (plus polarity in the present embodiment). The polarity is changed to positive polarity by positive polarity discharge by the transfer device 14g. Further, the surface side of the recording paper P is also positively charged by the positive polarity discharge by the secondary transfer device 14g, and the volume resistivity of the recording paper P is low, so that the positive charge is in the center or the back side (back side) of the recording paper P. It is also turning around. At this time, the potential of the recording paper P is charged to 1 to 2 kV with a positive polarity on the secondary transfer counter roller 14j across the intermediate transfer belt 14a.
[0080]
The recording paper P having a color toner image formed on the surface thereof has the same curvature as that of the curvature portion KT of the intermediate transfer belt 14a and the DC voltage applied to the end of the intermediate transfer belt 14a and applied to the secondary transfer device 14g. AC voltage Vp-p10 kV, 1 kHz applied with a DC voltage plus 500 V of polarity (plus polarity in this embodiment) is applied under the same conditions as when forming a double-sided image by a paper separation AC neutralizer 14 h as a transfer material separating means. The sheet is separated from the intermediate transfer belt 14a by the charge removing action and the separation claw 210, and is conveyed to the fixing device 17 as the fixing means through the spur 162, which is a spur member, at the time of double-sided image formation shown in FIG. Fixing is performed under the same fixing conditions. The recording paper P is positively charged at 200 to 700 V on the driving roller 14d.
[0081]
In the present embodiment, fixing is performed by the fixing means set under the same conditions during both-side image formation and front-side (single-side) image formation, and the toner image is held on the recording paper P for both the both-side image and the front-surface image. As a result, a good fixed image with no disturbance of the toner image can be obtained.
[0082]
(Image forming apparatus / other aspects)
Another embodiment of the image forming apparatus according to the present invention will be described with reference to FIG. FIG. 11 is a schematic explanatory diagram of a color image forming apparatus showing another embodiment of the image forming apparatus according to the present invention.
[0083]
In the image forming apparatus of this example, as shown in FIG. 11, a photosensitive drum 10b, which is a first image carrier that forms a toner image (back surface toner image) to be a back image, and a toner image (surface image). A photosensitive drum 10a, which is a second image carrier that forms a front surface toner image), is separately provided, and the back toner image formed on the photosensitive drum 10b is opposite in polarity to the toner (in this embodiment, a positive polarity). ) Is applied to the intermediate transfer belt 114a, which is an intermediate transfer member, by the primary transfer device B 114b to which a voltage of) is applied, and then the transfer material is transferred onto the intermediate transfer belt 114a between the photosensitive drum 10b and the photosensitive drum 10a. A certain recording paper P is supplied, and the recording paper P is charged by the paper charger 150 provided opposite to the earth roller 14k across the intermediate transfer belt 114a. The surface toner image formed on the photosensitive drum 10a by being sucked and conveyed is applied to the surface of the recording paper P by the primary transfer device A 114a to which a voltage having a polarity opposite to that of the toner (plus polarity in the present embodiment) is applied. After the transfer, the back side toner image on the intermediate transfer belt 114a is transferred to the back side of the recording paper P by the secondary transfer unit 114g to which a voltage having a polarity opposite to that of the toner (a positive polarity in the present embodiment) is applied. The recording paper P, on which the front and back toner images are formed on the recording paper P and the color toner images are formed on both sides, is applied to the curvature of the curvature portion KT of the intermediate transfer belt 114a and the end of the intermediate transfer belt 114a as necessary. The neutralization action by the paper separation AC neutralizer 14h as the transfer material separation means provided in the state, and the separation claw 210 provided in the transport unit 160 at a predetermined interval from the intermediate transfer belt 114a. Thus, the sheet is separated from the intermediate transfer belt 114a, conveyed to a fixing device 17 as a fixing unit through a spur 162 which is a spur member provided in the conveying unit 160, and between the first fixing roller 17a and the second fixing roller 17b. The toner image on the recording paper P is fixed at the nip portion T, and a double-sided image is obtained.
[0084]
The photosensitive drums 10a and 10b and the intermediate transfer belt 114a in the image forming apparatus of this example have the same function and structure as the photosensitive drum 10 and the intermediate transfer belt 14a described in the image forming apparatus. The intermediate transfer belt 114a is stretched in contact with a driving roller 14d, a ground roller 14j, a ground roller 14k, a driven roller 14e, a guide roller 14f, and a tension roller 14i, which are roller members. Further, the static eliminators 114m and 114n as the static eliminators are respectively connected to the primary transfer unit B 114b and the primary transfer unit A 114a after the primary transfer unit B 114b and the primary transfer unit A 114a with respect to the moving direction of the intermediate transfer belt 114a. The charge of the intermediate transfer belt 114a, which is provided in parallel and charged by applying the voltage of the primary transfer device B 114b and the primary transfer device A 114a, is applied with an alternating voltage superimposed with a direct current voltage of the same polarity or opposite polarity as the toner. Remove static electricity.
[0085]
Means for forming a toner image to be the back image on the photosensitive drum 10b as the first image carrier and means for forming the toner image to be the front image on the photosensitive drum 10a as the second image carrier. 4 sets of developing devices 13 (developing means) for the image forming process of yellow (Y), magenta (M), cyan (C) and black (K), similar to those used in the image forming apparatus described above. A scorotron charger 11 (charging means) and an exposure optical system 12 (image writing means) are used for the photosensitive drums 10b and 10a, respectively, to form a toner image of the back image and a toner image of the front image, respectively. .
[0086]
A color toner image of the front surface image (negative polarity in the present embodiment) formed on the photosensitive drum 10a by the recording paper P as a transfer material, and a color toner image of the back surface image carried on the intermediate transfer belt 114a. (Negative polarity in this embodiment) is synchronized and fed onto the intermediate transfer belt 114a, and a DC voltage having a polarity opposite to that of the toner (positive polarity in this embodiment) is applied in the transfer area. The surface image on the photosensitive drum 10a is transferred to the surface of the recording paper P at a time by the next transfer unit A114a. At this time, the intermediate transfer belt 114a (volume resistivity is 10 ⁸ -10 ¹² Since the surface toner image on the recording paper P is transferred across (Ω · cm), the surface toner image on the recording paper P is kept in the negative polarity without being converted in polarity. Further, after the charge of the intermediate transfer belt 114a charged to the positive polarity by the secondary transfer device 114c is discharged by the discharger 114n to which an AC voltage is applied, the back surface toner image on the intermediate transfer belt 114a is opposite to the toner. The image is transferred to the back surface of the recording paper P by the secondary transfer device 114g to which a DC voltage of polarity (positive polarity in the present embodiment) is applied. As in the case described with reference to FIG. 6, the back surface toner image on the recording paper P is kept in the negative polarity without being converted, but the negative polarity surface toner image on the recording paper P is The polarity is converted to positive polarity by positive polarity discharge by the secondary transfer unit 114g. Further, the surface side of the recording paper P is positively charged by the positive polarity discharge by the secondary transfer device 114g, and the volume resistivity of the recording paper P is low, so that the positive charge is in the center or back side (back side) of the recording paper P. ). At this time, the potential of the recording paper P is charged to 1 to 2 kV with a positive polarity on the secondary transfer counter roller 14j across the intermediate transfer belt 14a.
[0087]
The recording paper P on which the color toner images are formed on both sides is the same as the curvature of the curvature portion KT of the intermediate transfer belt 114a and the DC voltage applied to the end of the intermediate transfer belt 114a and applied to the secondary transfer device 114g. From the intermediate transfer belt 114a by the neutralization action by the paper separation AC static eliminator 14h as a transfer material separation means to which an alternating voltage superimposed with a direct current voltage of positive polarity (plus polarity in the present embodiment) is applied, and the separation claw 210. To be separated. The recording paper P is positively charged to 200 to 700 V on the driving roller 14d by the charge eliminating action. Next, it is conveyed to a fixing device 17 as fixing means through a spur 162 which is a spur member, and fixing is performed as described above.
[0089]
【The invention's effect】
Claim 1-2 According to the invention If In addition, the toner image is transferred onto the transfer material when fixing the single-sided image, as in the case of the double-sided image, by charging the secondary transfer unit used when forming the double-sided image. Therefore, a good fixed image with no disturbance of the toner image can be obtained.
[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 carrier in FIG.
FIG. 3 is an explanatory diagram illustrating a toner image forming state of a double-sided image.
FIG. 4 is an explanatory diagram showing a toner image forming state of a front surface (single side) image.
FIG. 5 is an explanatory diagram illustrating a structure of a fixing unit and a charging state of toner on a transfer material when a double-sided image is formed.
FIG. 6 is an explanatory diagram illustrating a transfer material that holds toner images on both sides immediately before fixing and a charged state of the toner.
FIG. 7 is an explanatory diagram illustrating a structure of a fixing unit and a charging state of toner on a transfer material during surface (single-sided) image formation.
FIG. 8 is an explanatory diagram showing a transfer material holding toner on the surface just before fixing and a charged state of the toner.
FIG. 9 Reference form Explanatory drawing which shows the fixing conditions.
FIG. 10 Embodiment Explanatory drawing which shows the state of the electric charge at the time of the surface (single side) image formation.
FIG. 11 is a schematic explanatory view showing another embodiment of the image forming apparatus according to the present invention.
[Explanation of symbols]
10, 10a, 10b Photosensitive drum
11 Scorotron charger
12 Exposure optics
13 Developer
14a, 114a Intermediate transfer belt
14c Primary transfer device
14g secondary transfer device
14h Paper separation AC static eliminator
14m, 114m, 114n
17 Fixing device
17a First fixing roller
17b Second fixing roller
P Recording paper

Claims (2)

An image carrier;
Means for forming a toner image on the image carrier;
An endless belt-shaped intermediate transfer body that can carry a toner image and supports and conveys a transfer material;
Primary transfer means for transferring the toner image on the image bearing member to the surface of the transfer material or the intermediate transfer member;
Secondary transfer means for transferring the toner image on the intermediate transfer member to the back surface of the transfer material;
Fixing means for fixing a transfer material carrying a toner image on the front surface or both front and back surfaces between fixing members;
In an image forming apparatus having
When the double-sided image is formed, the secondary transfer unit includes a charging step of transferring the backside toner image from the top surface toner image on the transfer material. Having a charging step similar to the above transfer for reversing the toner polarity on the transfer material,
After that, it is configured to perform static elimination and fixing,
The electric field condition applied between the fixing members at the time of double-sided image formation and the electric field condition applied between the fixing members at the time of surface image formation are the same, and between the fixing members for nipping and fixing the transfer material of the fixing unit An image forming apparatus, wherein the electric field formed in the step is an electric field in a direction to attract toner to a transfer material.   2. The image forming apparatus according to claim 1, wherein static elimination is performed at the time of separation of the transfer material from the intermediate transfer body even during surface image formation.

Images