JPH09297471A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten a first copying time and to prevent irregularities in a toner image by arranging an image carrying means, so as to place the center position of the distance between the centers of a driving roller and a driven roller, on the feeding side of a transfer material. SOLUTION: A transfer area 14b is provided and a toner image receptor 14a is arranged, in a state where the distance L1 between the middle position between both rollers and the center of a nip part formed as the transfer area 14b is placed on the side of the driving roller 14d by L/10-4L/10, with respect to the distance L between the center axes of the driving roller 14d and driven roller 14e of the toner image receptor 14a. A recording paper P is fed to the toner image receptor 14a along the lower guide plate 51 of a guiding means consisting of upper and lower guide plates 52 and 51. At this time, a position where the leading edge of the recording paper P fed along the lower guide plate 51 is abutted on the toner image receptor 14a is at least nearer to the side of a photoreceptor drum 10 than the center of the driven roller 14e to which the recording paper P is advanced. It is desirable that the abutting position is nearer to the drum 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copying machine which arranges a charging means, an image exposing means and a developing means 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 such as a printer, a FAX, or the like.

[0002]

2. Description of the Related Art Conventionally, in double-sided copying, an image on one side formed on an image carrier is transferred and fixed on a transfer material, and this is temporarily stored in a two-sided reversing paper feeder, and the image bearing is again performed. A method has been adopted in which a transfer material is fed from a double-sided reversing sheet feeder in synchronization with an image formed on the body, and an image on the other surface is transferred and fixed onto the transfer material.

In this double-sided copying apparatus, as described above, the transfer of the transfer material, such as feeding to the two-sided reversing paper feeder and passing through the fixing device twice, is performed, so that the reliability of transfer of the transfer material is low. And so on. In contrast, JP-B-49-37538 and JP-B-54-28740.
And JP-A-1-44457 and JP-A-4-21
Japanese Patent Application Laid-Open No. 4576/1994 proposes a method in which a toner image is formed on both surfaces of a transfer material and then fixed once.
JP-A-44457 and JP-A-4-214576 disclose that a plurality of sets of image forming means including an image carrier, a charging means, an image exposing means, a developing means and the like are arranged in parallel on a toner image receiving body. Has been proposed.

[0004]

However, Japanese Patent Application Laid-Open Nos. Hei 1-44457 and Hei 4-214576 mentioned above.
In the double-sided color image formation proposed in Japanese Patent Application Laid-Open Publication No. H08-27, the transferability of the transfer material is improved, but the color toner images are superimposed one by one on the toner image receiver, so that color misregistration, toner scattering and rubbing, etc. Image degradation easily occurs.

On the other hand, the inventors of the present invention once collectively transfer the toner images formed on the image carrier (first image carrier) to the toner image receiver (second image carrier), A double-sided image forming method is studied in which a toner image is formed again on the image carrier, and the toner image on the toner image receiver and the toner image formed again on the image carrier are transferred to both sides of the recording paper (transfer material). However, if the contact time between the recording paper and the toner images on both sides is long, there is a problem that a deviation between the recording paper and the toner image is likely to occur and good double-sided image formation is difficult. Further, the perimeter of the toner image receiver must be long enough to accommodate the maximum image size. If the toner image receiver is long, the transfer material transport length becomes long and the first copy time becomes slow. There's a problem. Further, as shown in FIG.
In order to obtain a good transfer of the double-sided toner image onto the recording paper P, the recording paper P fed through the guide means constituted by the upper guide plate 952 and the lower guide plate 951 respectively bears the toner image on the image carrier 910. And the toner image receiver 914a, and when trying to feed toward the transfer area 914b of the transfer device 914c, the leading end of the recording paper P is shaken until the recording paper P reaches the transfer area 914b. The toner image on the body 910 or the toner image on the toner image receiving body 914a is contacted and disturbs each toner image, or the recording paper P is fed along the upper surface of the lower guide plate 951 from the front end thereof. The recording paper P to be fed due to a long interval up to the transfer area 914b.
Is attached to the side of the image carrier 910 or a toner image receiver 914a
We have found a phenomenon in which the toner images on the side disturb each toner image and a good double-sided image is not formed. It was also confirmed that the recording paper P is greatly shaken even when the trailing edge of the recording paper P is passed, and the toner image is disturbed.

The present invention solves the above problems, makes it difficult for the transfer material to be displaced from the toner images on both sides thereof, shortens the first copy time, and allows the transfer material to be transferred to the transfer area without disturbing the toner image. It is an object of the present invention to provide an image forming apparatus that is fed to and forms a good double-sided image.

[0007]

SUMMARY OF THE INVENTION The above-mentioned object is to combine a first image carrying means for carrying a toner image formed by a toner image forming means and a toner image carried by the first image carrying means together. Second image carrying means for carrying the transferred toner image on the surface again, and first transfer carrying the toner image carried on the first image carrying means on the surface of the transfer material. Means, a second transfer means for transferring the toner image carried by the second image carrying means to the back surface of the transfer material, and a first transfer means carrying the toner image on the first image carrying means. The toner image formed on the transfer material is transferred to the surface of the transfer material, and the toner image carried on the second image carrying means is transferred to the back surface of the transfer material by the second transfer means. And fixing means for fixing the toner images transferred on both sides of the In the image forming apparatus, the second
The image bearing means is a belt-shaped member stretched by at least a driving roller and a driven roller, and the center position of the interval between the center of the driving roller and the center of the driven roller with respect to the transfer position by the first transfer means. This is achieved by an image forming apparatus characterized in that the second image carrier is arranged so as to be located on the feeding side of the transfer material.

[0008]

Embodiments of the present invention will be described below. Note that the description in this column does not limit the technical scope of the claims and the meaning of terms. Also, the following assertive description in the embodiment of the present invention indicates the best mode, and does not limit the meaning of the terms of the present invention or the technical scope. In the following description of the embodiment, when a color toner image is transferred to a transfer material, an image to be transferred to a surface of the transfer material facing the image carrier in the transfer area (referred to as a surface of the transfer material) will be described. The front image and the image transferred to the other surface of the transfer material (called the back surface of the transfer material) are called the back surface image.

The image forming process and each mechanism of one embodiment of the image forming apparatus of the present invention will be described with reference to the color image forming apparatus shown in FIGS. FIG. 1 is a sectional configuration diagram of a color image forming apparatus showing one embodiment of the present invention, FIG. 2 is a side sectional view of the image carrier of FIG.
FIG. 4 is a diagram showing a toner image formation state on both sides, and FIG.
FIG. 3 is a diagram showing a method of entering a transfer material into a toner image receiver.
FIG. 5 is a diagram showing a first example of the charging process of the transfer material charging means.

The photosensitive drum 10 serving as an image carrier has a cylindrical base formed of, for example, a transparent member such as optical glass or transparent acrylic resin provided inside, and a transparent conductive layer,
A photosensitive layer such as an a-Si layer or an organic photosensitive layer (OPC) is formed on the outer periphery of the substrate, and is rotated clockwise as shown by an arrow in FIG. 1 in a grounded state.

As shown in FIG. 2, the photosensitive drum 10 has flange members 10a and 10b at both ends for engaging and fixing it.
Is rotatably supported by bearings 110a and 110b fitted in flange members 10a and 10b at both ends of a drum shaft 110 that is erected and fixed to the main body of the apparatus. It is rotated at a constant speed in a predetermined direction by being driven by meshing with a drive gear on the apparatus main body side.

Scorotron charger 11 as charging means
Is used in an image forming process of each color of yellow (Y), magenta (M), cyan (C) and black (K), and is exposed in a direction orthogonal to a moving direction of the photosensitive drum 10 as an image carrier. It is installed facing the body drum 10,
A charging operation is performed by a control grid maintained at a predetermined potential with respect to the above-described organic photoconductor layer of the photoconductor drum 10 and a corona discharge having the same polarity as the toner using, for example, a sawtooth electrode as the discharge electrode 11a (this embodiment). , A uniform potential is applied to the photosensitive drum 10. Other wire electrodes can be used as the discharge electrode 11a.

The exposure unit 12 as an image exposing means for each color is arranged such that the exposure position on the photosensitive drum 10 is between the discharge electrode 11a of the scorotron charger 11 and the developing position of the developing device 13 and a developing sleeve 131. With respect to the photoconductor drum, the photoconductor drum is arranged on the upstream side in the rotation direction.

The exposure unit 12 is a linear exposure element 12a in which a plurality of LEDs (light emitting diodes) as image exposure light emitting elements arranged in the main scanning direction in parallel with the axis of the photosensitive drum 10 are arranged in an array. And a SELFOC lens 12b as an equal-magnification imaging element are configured as an exposure unit attached to a holder (not shown). Holding member 20
The exposure unit 12, the uniform exposure unit 12c, and the simultaneous transfer exposure unit 12d for each color are attached to the
Of the substrate. The image data of each color read by a separate image reading device and stored in the memory is sequentially read from the memory, and the exposure unit 1 for each color
2 are respectively input as electric signals.

As the exposure element, a plurality of light emitting elements such as FL (fluorescent substance emission), EL (electroluminescence), PL (plasma discharge), LED (light emitting diode) and the like arranged in an array are used. The emission wavelength of the light emitting element used in this embodiment is usually Y, M, C
In the range of 680 to 900 nm, which has a high toner transparency, is preferable, but a shorter wavelength may be used because the color toner does not have sufficient transparency because image exposure is performed from the back surface.

A developing unit 13 provided in accordance with the color sequence in which an image is formed and the rotating photosensitive drum is provided in accordance with the color sequence.
In the present embodiment, the developing units 13 for Y and M are on the left side of the photosensitive drum 10 with respect to the rotation direction of the photosensitive drum 10 indicated by the arrow in FIG. Are arranged on the right side of the photosensitive drum 10 and the Y and M developing devices 1
3 and a scorotron charger 11 for C and K above the developing casing 138 of the developing unit 13 for C and K, respectively.
Is arranged.

The developing device 13 as a developing means for each color includes
One-component or two-component developers of yellow (Y), magenta (M), cyan (C) and black (K) are accommodated, respectively, and a predetermined gap is maintained with respect to the peripheral surface of the photosensitive drum 10, respectively. At the developing position, the photosensitive drum 10 rotates in the same direction as the rotating direction of the photosensitive drum 10.
The developing sleeve 131 is made of cylindrical non-magnetic stainless steel or aluminum and has an outer diameter of 15 to 25 mm.

The developing device 13 is provided with an abutting roller (not shown) and a gap of a predetermined value from the photosensitive drum 10, for example, 100 μm.
.About.1000 .mu.m and kept in a non-contact state, and when developing by the developing device 13 for each color, the developing sleeve 131
A developing bias to which a DC voltage or an AC voltage AC is further applied is applied to the photosensitive drum, a jumping development is performed with a one-component or two-component developer contained in the developing device, and a negatively charged photosensitive member grounds the transparent conductive layer. The same polarity as the toner for the drum 10 (minus polarity in this embodiment)
Is applied, and non-contact reversal development is performed in which toner is adhered to an exposed portion. At this time, the precision of the development interval needs to be about 20 μm or less in order to prevent image unevenness.

The developing device 13 for each color applies a developing bias voltage to the electrostatic latent image on the photosensitive drum 10 formed by the charging by the scorotron charger 11 and the image exposure by the exposure unit 12. (In the present embodiment, the photosensitive drum is negatively charged,
Reversal development is carried out with a negative polarity toner).

An image read by an image sensor of an image reading apparatus separate from the apparatus or an image edited by a computer is temporarily stored as image data for each of Y, M, C and K as an original image. And stored.

A gear 10 provided on the rear flange 10b of the photoconductor drum 10 is driven through a drive gear G1 by starting a photoconductor drive motor (not shown) when image recording is started.
G is rotated to rotate the photosensitive drum 10 in the clockwise direction indicated by the arrow in FIG. 1, and at the same time, Y disposed below the developing casing 138 of the yellow (Y) developing device 13 to the left of the photosensitive drum 10. The application of a potential to the photosensitive drum 10 is started by the charging action of the scorotron charger 11 described above.

After a potential is applied to the photosensitive drum 10, exposure is started by a first color signal, that is, an electric signal corresponding to the Y image data in the Y exposure unit 12, and the surface of the photosensitive drum 10 is exposed by rotational scanning of the drum. An electrostatic latent image corresponding to the Y image of the original image is formed on the layer.

The latent image is reversal-developed by the Y developing device 13 in a state where the developer on the developing sleeve is not in contact with the developer, and a yellow (Y) toner image is formed in accordance with the rotation of the photosensitive drum 10.

Next, the photosensitive drum 10 is placed on the magenta (M) developing unit 1 on the yellow (Y) toner image and further on the left of the photosensitive drum 10 and above the yellow (Y).
A potential is applied by the charging action of the magenta (M) scorotron charger 11 arranged below the developing casing 138 of No. 3, and the electric signal corresponding to the second color signal of the M exposure unit 12, that is, the image data of M. Exposure is performed by non-contact reversal development by the developing device 13 of M, and magenta (M) is formed on the yellow (Y) toner image.
Toner images are sequentially superposed and formed.

By the same process, the developing casing 13 of the cyan (C) developing device 13 is provided on the right side of the photosensitive drum 10.
The cyan (C) toner image corresponding to the third color signal is further obtained by the cyan (C) scorotron charger 11, the exposure unit 12 of C, and the developing unit 13 of C, which are arranged above the photoconductor 8 The black (K) scorotron charger 11, the exposure unit 12, and the developing device 13 are arranged on the right side of the drum 10 and below the developing casing 138 of the black (K) developing device 13 at the lower part of the fourth color by the fourth unit. A black (K) toner image corresponding to the signal is sequentially superposed, and a color toner image is formed on the peripheral surface within one rotation of the photosensitive drum 10 (toner image forming means).

Exposure unit 1 for Y, M, C and K
Exposure of the organic photosensitive layer of the photosensitive drum 10 by 2 is performed from the inside of the drum through the transparent substrate described above. Therefore, the exposure of the images corresponding to the second, third, and fourth color signals is performed without any influence from the previously formed toner image, and the same exposure as the image corresponding to the first color signal is performed. It is possible to form an electrostatic latent image.

By the above-described image forming process, a superimposed color toner image serving as a back surface image is formed on the photosensitive drum 10 (first image carrying means) serving as an image carrier. The transfer roller 14c to which a DC voltage having the opposite polarity (positive polarity in the present embodiment) is applied to the superposed color toner image in the transfer area 14b by the driving roller 14d and the driven roller 1
4e, and is collectively transferred onto a toner image receiving member 14a (second image carrying means) provided in proximity to or in contact with the photosensitive drum 10. At this time, for example, uniform exposure is performed by the simultaneous transfer exposure device 12d using a light emitting diode so that good transfer is performed.

The toner remaining on the peripheral surface of the photosensitive drum 10 after the transfer is subjected to static elimination by the image carrier AC static eliminator 16 and then enters the cleaning device 19 or the photosensitive drum 10.
Cleaning blade 19a made of a rubber material abutting against
In order to eliminate the history of the photoreceptor up to the previous print, the peripheral surface of the photoreceptor is removed by, for example, exposure by a uniform exposure unit 12c before charging using a light emitting diode, and the charge at the previous print is removed. Is removed and the next color image formation of the front surface image is performed.

The back side image formed on the toner image receiving body 14a and the transfer area 14b are synchronized with each other, and the front side image of the superimposed color toner image is formed on the photosensitive drum in the same manner as in the above-mentioned color image forming process. Formed on 10. It is necessary to change the image data so that the front side image formed at this time is a mirror image of the back side image formation on the image carrier.

The transfer sheet P, which is a transfer material, is sent out from the paper feed cassette 15 which is a transfer material storage means by the sending roller 15a, is fed by the feeding roller 15b, and is conveyed to the timing roller 15c.

The recording paper P is driven by the timing roller 15c to form a color toner image of a front surface image carried on the photosensitive drum 10 and a color toner image of a rear surface image carried on the toner image receiver 14a. Are fed to the transfer area 14b in synchronization with the above. At this time, the recording paper P is charged to the same polarity as the toner by the paper charger 14f as the transfer material charging means, adsorbed to the toner image receiving body 14a, and fed to the transfer area 14b. By charging the paper with the same polarity as that of the toner, it is possible to prevent the toner image on the toner image receiving body and the toner image on the image carrier from being attracted to each other, thereby preventing the toner image from being disturbed. Further, as the transfer material charging unit, a conductive roller, a brush charger, or the like, which can be brought into contact with and released from the toner image receiver, can be used.

A surface image on the peripheral surface of the photosensitive drum 10 is collectively recorded on a recording paper by a transfer unit 14c as a first transfer unit to which a voltage having a polarity opposite to that of the toner (positive polarity in the present embodiment) is applied. It is transferred to the upper surface side (front side) of P. At this time, the back surface image on the peripheral surface of the toner image receiver 14a is not transferred to the recording paper P but exists on the toner image receiver 14a. Next, a backside image on the peripheral surface of the toner image receiving body 14a is collectively recorded by a backside transfer unit 14g as a second transfer unit to which a voltage having a polarity opposite to that of the toner (positive polarity in the present embodiment) is applied. The image is transferred to the lower surface (back surface) of the paper P. At the time of transfer by the transfer device 14c, uniform exposure is performed by a simultaneous transfer exposure device 12d using, for example, a light emitting diode, provided inside the photosensitive drum 10 so as to perform good transfer so as to face the transfer device 14c. Is performed.

Since the toner images of the respective colors are overlapped with each other, it is preferable that the upper layer toner and the lower layer toner are charged with the same charge amount and the same polarity to enable batch transfer. Therefore, in a double-sided image formation in which the polarity of the color toner image formed on the toner image receiving member 14a is inverted by corona charging or the polarity of the color toner image formed on the image carrier is inverted by corona charging, the lower layer is formed. The toner is not sufficiently charged to the same polarity, so that the transfer becomes unfavorable.

The reversal development is repeated on the image carrier, and the color toner images of the same polarity formed by superimposition are collectively transferred to the toner image receiver 14a without changing the polarity, and then the recording paper is changed without changing the polarity. The batch transfer to P is preferable because it contributes to the improvement of the transferability of the backside image formation. Also for the surface image formation, reversal development is repeatedly performed on the image carrier, and the color toner images of the same polarity formed by superimposition are collectively transferred to the recording paper P without changing the polarity. It is preferable because it contributes to improvement of the property.

As described above, in the color image formation, the first transfer means is operated to form a color toner image on the surface of the transfer material by using the above-described front and back surface image forming method. A two-sided image forming method of forming a color toner image on the back surface of the transfer material by operating the second transfer means is preferably employed.

The toner image receiver 14a has a thickness of 0.5-2.
An endless rubber belt of 0 mm, a semiconductive substrate of silicon rubber or urethane rubber having a resistance value of 10 ⁸ to 10 ¹² Ω · cm, and a thickness of 5 to 50 μm as a toner filming prevention layer outside the rubber substrate. And a two-layer structure with fluorine coating. This layer also preferably has a similar semiconductivity. 0.1-0.5 thickness instead of rubber belt base
mm semiconductive polyester, polystyrene, polyethylene, polyethylene terephthalate, or the like can also be used.

The recording paper P on which the color toner images are formed on both sides is discharged by a paper separation AC discharger 14h for separating the transfer material, separated from the toner image receiver 14a, and a heater is provided inside both rollers. The sheet is conveyed to a fixing device 17 as a fixing unit including two rollers.
By applying heat and pressure between the fixing roller 17a and the pressure roller 17b, the toner adhered to the front and back of the recording paper P is fixed, and the recording paper P on which double-sided image recording has been performed is sent by the paper discharge roller 18. And discharged to a tray outside the apparatus.

The toner remaining on the peripheral surface of the toner image receiver 14a after the transfer is brought into contact with and abuts on the toner image receiver 14a provided in a toner image receiver cleaning device 14i as cleaning means for the toner image receiver. It is cleaned by a blade that can be released. The toner remaining on the peripheral surface of the photoconductor drum 10 after the transfer is subjected to static elimination by the image carrier AC static eliminator 16, and then enters a cleaning device 19 or is made of a rubber material that abuts on the photoconductor drum 10. Cleaning device 1 by cleaning blade 19a
9 and is collected by a screw 19b into a waste toner container (not shown). The photoconductor drum 10 from which the residual toner has been removed by the cleaning device 19 is uniformly charged by the Y scorotron charger 11, and enters the next image forming cycle.

By using the above-described method, since the superimposed color toner images are transferred collectively, color shift of the color image on the toner image receiving member, scattering or rubbing of the toner, and the like are less likely to occur, and the image is less deteriorated. A double-sided color image is formed.

In the above image forming apparatus, it is needless to say that only one side is copied by the first image carrying means or the second image carrying means.

A first example of feeding the transfer material will be described with reference to FIGS. 4 and 5, but as shown in FIG.
The transfer area 1 on the transfer device 14c as the first transfer means so that the toner image of the front surface image on 0 is transferred favorably.
It is preferable that the toner image receiving body 14a is formed in contact with the photoconductor drum 10 by using 4b as a nip portion.
The angle θ formed by the central axis of the photoconductor drum 10 and the half-value width of the nip portion is preferably 7.5 ° to 14 ° so that the recording paper P as the transfer material can smoothly enter the nip portion. When the angle θ is 7.5 ° or less, good transfer is not performed, and when the angle θ is 14 ° or more, bending or bending occurs when the transfer material enters.

The recording paper P is brought into close contact with the toner image of the back side image on the toner image receiving body 14a and conveyed to the back side transfer device 14g as the second transfer means through the transfer area 14b. It is preferable that the distance to the separation portion provided with the paper separation AC static eliminator 14h above 14d is shorter because the toner images on both sides and the recording paper P are conveyed without deviation. Therefore, with respect to the distance L between the center axes of the driving roller 14d and the driven roller 14e of the toner image receiving body 14a having the maximum image size, for example, the A-3 size, which is required to carry the intermediate length of both rollers. Position and transfer area 14
The distance L1 from the center of the nip formed as b is L /
A transfer area 14b is provided closer to the drive roller 14d side by 10 to 4 L / 10, and the toner image receiving body 14a is arranged.

The recording paper P is fed to the toner image receiving body 14a along the lower guide plate 51 of the guide means formed by the upper guide plate 52 and the lower guide plate 51.
The shorter the time it takes for the toner image to come into close contact with the toner image of the back side image on the toner image receiving body 14a, the closer the toner image is made without disturbing the toner image, the leading edge of the recording paper P fed along the lower guide plate is It is preferable that the position of contact with the toner image receiving body 14a is at least closer to the photosensitive drum than the center of the driven roller 14e into which the recording paper P enters and closer to the photosensitive drum 10. That is, as described above, the distance from the transfer area 14b to the separating portion is shortened, and the recording paper P is further transferred to the transfer area 1
The first copy time is shortened because the toner is transferred to the toner image receiving body 14a in close proximity to the sheet 4b.

Further, the driving roller 14d and the driven roller 14
An angle β formed between the belt surface of the toner image receiving body 14a stretched over the e and the surface of the lower guide plate 51 into which the recording paper P enters.
Is preferably 5 ° to 20 °. When the angle β is 5 ° or less, the adhesion between the recording paper P and the toner image receiving body 14a is not good, and when it is 20 ° or more, the recording paper P is caught on the toner image receiving body 14a.

Due to the above, the contact time between the transfer material and the toner images on both sides is short, and good double-sided image formation can be performed without causing a deviation between the transfer material and the toner image. Further, the toner image of the surface image on the photosensitive drum 10 and the recording paper P are transferred to the transfer area 14
Since the toner image of the front surface image is kept in contact until just before b, the toner image of the front surface image is not disturbed and is also transferred onto the recording paper P by the transfer device 14c together with the recording paper P.

As shown in FIG. 5, the paper charger 14f serving as the transfer material charging means includes a toner for the paper charger 14f when the recording paper P enters the toner image receiver 14a with the leading edge of the back side image. Bias voltage E1 of -500 to -2 kVDC of the same polarity (negative polarity in this embodiment)
Is applied and the bias voltage E1 is continuously applied during the passage of the recording paper P, and the application of the bias voltage E1 is cut off at the same time as or immediately after the passage of the recording paper P. At this time, the driven roller 14
e is grounded.

The driven roller 14e and the paper charger 1 which are grounded
The recording paper P charged in the negative polarity is attracted to the toner image receiving body 14a by the positive charging induced in the toner image receiving body 14a by the application of the bias voltage E1 having the same polarity as the toner applied to 4f. Be transported. At this time, since the recording paper P is charged with a negative polarity and is conveyed, the toner image receiver 14a having a negative charge.
The upper toner or the toner on the photoconductor drum 10 having a negative charge is repelled by the negative charge of the recording paper P, and the toner (negative polarity) shown in FIG. 5 is attracted to the recording paper P. This does not occur, and in particular, image disturbance due to toner movement that occurs when the recording paper P has a positive polarity does not occur.

As another bias voltage applying method,
The same charging effect can be obtained even if the transfer material charging means is grounded and the application of a voltage of the same polarity as that of the toner is applied to the driven roller 14e.

The transfer device 14c as the first transfer means transfers the recording paper P conveyed to the recording paper P through the toner image receiving body 14a as the second image carrying means, which has a polarity different from that of the toner (plus polarity in this embodiment). By applying a voltage, the toner image on the photoconductor drum 10 as the first image carrying means is transferred onto the surface of the recording paper P as the transfer material, and then by the back surface transfer device 14g as the second transfer means. The surface of the recording paper P is charged with a different polarity (in the present embodiment, a positive polarity) from the toner, and the toner image on the toner image receiving body 14a as the second image carrying means is transferred to the back surface of the recording paper P. Then, double-sided image formation is performed.

As described above, the recording paper is satisfactorily adhered to the toner image receiving body, the toner is prevented from moving to the recording paper, and excellent double-sided transfer is performed.

A second example of feeding the transfer material will be described with reference to FIGS. 6 and 7. FIG. 6 is a diagram showing a method of introducing the transfer material into the photosensitive drum, and FIG. 7 is a diagram showing a second example of the charging process of the transfer material charging means.

As described with reference to FIG. 4, the angle θ formed between the center of the photosensitive drum 10 and the half width of the nip portion is 7.5 °.
-14 ° is preferred.

The recording paper P is conveyed to the transfer area 14b in close contact with the toner image of the surface image on the photosensitive drum 10, and a paper separation AC static eliminator 14h is provided above the drive roller 14d from the transfer area 14b. It is preferable that the distance to the separating portion is shorter because the toner images on the both surfaces and the recording paper P can be conveyed without deviation. Therefore, with respect to the distance L between the centers of the driving roller 14d and the driven roller 14e of the toner image receiving body 14a,
The distance L1 between the intermediate position of both rollers and the center of the nip formed as the transfer area 14b is L / 10 to 4L / 10, and the transfer area 14b is provided closer to the driven roller 14e side to provide the toner image receiver. 14a is arranged.

The recording paper P is fed to the photosensitive drum 10 along the guide portion 151a of the lower guide plate 151 of the guide means formed by the upper guide plate 152 and the lower guide plate 151. The shorter the time it takes for the toner image of the surface image on the photoconductor drum 10 to come into close contact with the toner image, the closer the toner image will be without disturbing the toner image, so the guide portion 1 of the lower guide plate 151.
The position where the front end of the recording paper P fed along 51a abuts on the photoconductor drum 10 is preferably closer to the transfer area 14b on the peripheral surface of the photoconductor drum 10, and is perpendicular to the center axis of the photoconductor drum 10. The angle formed by the line and the contact portion of the recording paper P on the photosensitive drum 10 is α1, and the guide portion 1 of the lower guide plate 151 is
When the angle between the upper surface of the recording paper P fed along 51a and the contact portion of the recording paper P with the photoconductor drum 10 is α2, the angle α1 is 28 ° to 32 °, which is the angle with respect to the angle α1. α2 is preferably 57 ° to 53 °. If the angle α1 is 28 ° or less and the angle α2 is 57 ° or more, the adhesion between the recording paper P and the photosensitive drum 10 is not good, and the angle α1 is 32.
When the angle α2 is 53 ° or more and the angle α2 is 53 ° or less, the recording paper P is caught on the photosensitive drum 10. If the distance L2 between the bent portion 151c of the lower guide plate 151 and the peripheral surface of the photosensitive drum 10 is 0.5 mm to 2 mm, and the length L3 of the bent portion 151b is 3 mm to 5 mm, the recording paper P will not enter. Made smooth and preferable.

As described above, the distance from the transfer area 14b to the separating portion is shortened, and the recording paper P is transferred to the transfer area 14b.
The first copy time is shortened because the toner image receiver 14a is conveyed closer to the sheet and is conveyed. Further, the contact time between the transfer material and the toner images on both sides is short, and good double-sided image formation is carried out without causing a deviation between the transfer material and the toner image. Further, since the toner image of the back side image on the toner image receiving body 14a and the recording sheet P are kept in non-contact until just before the nip portion as the transfer area 14b, the toner image of the back side image is not disturbed and the recording sheet is not disturbed. It is combined with P and is transferred onto the recording paper P by the back surface transfer device 14g through the transfer area 14b above the transfer device 14c.

As shown in FIG. 7, when the recording paper P is aligned with the leading edge of the front surface image and enters the photosensitive drum 10,
As a transfer material charging unit, the lower guide plate 151 has the same polarity (negative polarity in the present embodiment) of −500 to that of the toner.
A bias voltage E2 of −2 kVDC is preferably applied, and the bias voltage E2 is continuously applied during passage of the recording paper P, and the application of the bias voltage E2 is cut off at the same time as or immediately after the passage of the recording paper P.

Photoreceptor drum 10 and paper charger 1 which are grounded
By applying a bias voltage E2 having the same polarity as the toner applied to 4f and a negative polarity, the recording paper P is moved to the photosensitive drum 1
It is adsorbed by 0 and conveyed. At this time, since the recording paper P is charged with a negative polarity and conveyed, the toner on the photosensitive drum 10 having a negative charge or the toner on the toner image receiving body 14a having a negative charge is negatively charged on the recording paper P. 7, the toner (minus polarity) as shown by the dotted line in FIG. 7 is not attracted to the recording paper P, and the image is disturbed due to the toner movement that occurs especially when the recording paper P is made to have the positive polarity. Absent. As the transfer material charging means, a conductive brush may be attached to a guide member, and a voltage may be applied to this to charge the recording paper P.

A transfer device 14c as a first transfer means transfers the recording paper P conveyed to the recording paper P through a toner image receiving body 14a as a second image carrying means, which has a polarity different from that of the toner (plus polarity in this embodiment). By applying a voltage, the toner image on the photoconductor drum 10 as the first image carrying means is transferred onto the surface of the recording paper P as the transfer material, and then by the back surface transfer device 14g as the second transfer means. The surface of the recording paper P is charged with a different polarity (in the present embodiment, a positive polarity) from the toner, and the toner image on the toner image receiving body 14a as the second image carrying means is transferred to the back surface of the recording paper P. Then, double-sided image formation is performed.

As described above, the toner transfer to the recording paper is prevented, and good double-sided transfer is performed.

Although the present invention has been described using the color image forming apparatus, it is needless to say that the present invention can be applied to a monochrome image forming apparatus. Further, the present invention includes not only the present method but also a modified example of forming a double-sided image.
Japanese Patent Application Laid-Open Nos. 63-180969 and 63-2, in which after inverting the polarity of the toner corresponding to the backside image shown in JP-A-28740, the toner is simultaneously transferred to both sides of the transfer material.
In the tandem method of JP-A-98255 and JP-A-1-44457, changing the process conditions and image data processing conditions between the front surface and the back surface as described above is used, and the image density and color tone are adjusted. And a double-sided image can be formed.

Further, in the above embodiment, the outer diameter of the drive roller and the outer diameter of the driven roller are not necessarily the same, and different outer diameters may be used.

[0062]

According to the first aspect of the present invention, the contact time between the transfer material and the toner images on both sides is short, and good double-sided image formation can be performed without causing a deviation between the transfer material and the toner image. Also, the first copy time is shortened.

According to the second aspect of the present invention, one surface of the transfer material is surely brought into close contact with the second image carrying means, and is aligned with the toner image on the second image carrying means before being fed to the transfer area. Toner transfer to the transfer material is prevented, and good transfer is performed on both surfaces of the transfer material without disturbing the toner image on the first image carrier.

According to the third aspect of the present invention, one side of the transfer material is surely brought into close contact with the first image carrying means, and is aligned with the toner image on the first image carrying means before being fed to the transfer area. Toner transfer to the transfer material is prevented, and good transfer is performed on both surfaces of the transfer material without disturbing the toner image on the second image carrier.

[Brief description of drawings]

FIG. 1 is a cross-sectional configuration diagram of a color image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a side sectional view of the image carrier of FIG. 1;

FIG. 3 is a diagram illustrating a state where toner images are formed on both surfaces.

FIG. 4 is a diagram illustrating a method of entering a transfer material into a toner image receiving body.

FIG. 5 is a diagram illustrating a first example of a charging process of a transfer material charging unit.

FIG. 6 is a diagram showing a method of introducing a transfer material into a photosensitive drum.

FIG. 7 is a diagram illustrating a second example of a charging process of a transfer material charging unit.

FIG. 8 is a diagram showing a problem of the present invention.

[Explanation of symbols]

 10 Photoconductor Drum 11 Scorotron Charger 12 Exposure Unit 13 Developing Device 14a Toner Image Receptor 14b Transfer Area 14c Transfer Device 14d Drive Roller 14e Driven Roller 14g Back Transfer Device 14h Paper Separation AC Static Electrifier 17 Fixing Device 51, 151 Lower Guide Plate 52,152 Upper guide plate E1, E2 Bias voltage P Recording paper

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Akira Matsubara Konica Corporation, 2970 Ishikawacho, Hachioji-shi, Tokyo (72) Inventor Tadayoshi Ikeda 2970, Ishikawacho, Hachioji-shi, Tokyo Konica Corporation (72) Invention Person Masakazu Fukuchi 2970 Ishikawacho, Hachioji-shi, Tokyo Konica Corporation

Claims (3)

[Claims] 1. A first image bearing means for bearing a toner image formed by a toner image forming means, and a toner image carried on the first image bearing means are collectively transferred and transferred. Second image carrying means for carrying the toner image again on the surface; first transfer means for transferring the toner image carried by the first image carrying means onto the surface of a transfer material; and the second image Second transfer means for transferring the toner image carried by the carrying means onto the back surface of the transfer material; and the toner image carried by the first image carrying means by the first transfer means for the transfer material. Of the toner image transferred to the front surface of the transfer material, and the toner image carried by the second image carrying means by the second transfer means to the back surface of the transfer material, and the toner image transferred to both surfaces of the transfer material. In an image forming apparatus having a fixing unit for fixing The second image bearing means is a belt-shaped member stretched by at least a driving roller and a driven roller, and a distance between the center of the driving roller and the center of the driven roller is set with respect to the transfer position of the first transfer means. An image forming apparatus, wherein the second image bearing means is arranged such that a center position thereof is located on a feeding side of the transfer material. 2. A guide means for advancing the transfer material into the second image carrying means is provided in the vicinity of the second image carrying means, and the first image carrying means and the second image carrying means are provided. When the transfer material enters between the first transfer member and the second transfer member, the guide member causes the leading end of the transfer material to come into contact with the second image carrying unit first, and the transfer material charging unit that charges the transfer material transfers the transfer material. The image forming apparatus according to claim 1, wherein the material is charged to have the same polarity as the toner, and the material is brought into intimate contact with the second image bearing unit. 3. A guide means for causing the transfer material to enter the first image carrying means is provided in the vicinity of the first image carrying means, and the first image carrying means and the second image carrying means are provided. When the transfer material enters between the transfer material and the transfer material, the transfer material charging means first brings the transfer material leading end into contact with the first image carrying means, and the guide means causes the transfer material to move together with the toner. The image forming apparatus according to claim 1, wherein the image forming apparatus is charged with a polarity, and the transfer material is brought into intimate contact with the first image bearing unit.