JPH09297468A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the movement of toner to a transfer material and to obtain an excellent both-side image by surely, closely sticking one side of the transfer material to an image carrier means, so as to align the transfer material with a toner image on the image carrying means and then, feeding the transfer material to a transfer area. SOLUTION: A recording paper P is fed to a toner image receptor 14a on a driven roller 14e, 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 fed recording paper P is abutted on the toner image receptor 14a is as follows: the leading edge is abutted at intervals of L2 on the upstream side and L1 on the downstream side in the feeding direction of the recording paper P, from the center of the driven roller 14e. When the recording paper P is aligned with the top end of a rear side image and advanced to the toner image receptor 14a, a bias voltage having the same polarity (negative polarity) as that of the toner is applied to a paper electrifier 14f. Thus, the recording paper P electrified to the negative polarity is attracted to the toner image receptor 14a by positive electrification induced in the toner image receptor 14a, to be carried.

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. On the other hand, JP-B-49-37538, JP-B-54-28740, JP-A-1-44457, and JP-A-4-214576 are used to form a toner image on both surfaces of the transfer material, and then fixing is performed once. However, the image carrier, the charging means, and
There has been proposed a method of forming a two-sided copy of a color image by arranging image forming means including an image exposing means and a developing means in parallel on a plurality of toner image receiving members.

[0004]

However, in the double-sided color image formation proposed by the above-mentioned JP-A-1-44457 and JP-A-4-214576, the transfer material transportability is improved, but the toner image receiving is improved. Since the color toner images are superposed one by one on the body, image deterioration such as color misregistration, toner scattering, and rubbing easily occurs.

On the other hand, as shown in FIG. 7, the inventors of the present invention once provided the toner image formed on the image carrier (first image carrier) 910 with the toner image receiver (second image carrier). )
A toner image is formed on the image bearing member 910 again by collectively transferring to the image bearing member 914a, and the toner image on the toner image receiving member 914a and the toner image formed again on the image bearing member 910 are used as recording paper (transfer material). A double-sided image forming method of transferring the double-sided toner image to the both sides of P is being studied, but in order to obtain a good transfer of the double-sided toner image onto the recording paper P, a guide means composed of an upper guide plate 952 and a lower guide plate 951. Recording paper P fed through
To the transfer area 914b of the transfer device 914c by aligning them with the image carrier 910 and the toner image receiver 914a respectively carrying the toner image.
Before the recording paper P reaches b, the leading end of the recording paper P is shaken and the toner image on the image carrier 910 or the toner image receiver 91.
The toner image on the recording sheet P is disturbed by contacting the toner images on the recording sheet 4a, or the recording sheet P is fed along the upper surface from the leading end of the lower guide plate 951 to the transfer area 914b. It has been found that the recording paper P is adhered to the image carrier 910 side or the toner image receiver 914a side to disturb the respective toner images and a good double-sided image is not formed. Also, it was confirmed that the toner image is disturbed even when the recording paper P is largely shaken when the trailing edge of the recording paper P is passed.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above problems and to provide an image forming apparatus in which a transfer material is fed to a transfer area without disturbing a toner image and a good double-sided image is formed. .

[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
Guide means for advancing the transfer material between the first image carrying means and the second image carrying means in the vicinity of the first image carrying means and the second image carrying means. When the transfer material enters the space between the image carrier and the image carrier, the leading edge of the transfer material is brought into contact with the second image carrier by the guide means, and the transfer material is charged to the same polarity as the toner. Then, it is achieved by an image forming apparatus characterized in that the second image carrying means is brought into close contact with the second image bearing means (first invention).

The above object is also achieved by a first image holding means for holding a toner image formed by a toner image forming means,
The toner images carried by the first image carrying device are collectively transferred, and the second image carrying device carrying the transferred toner image again on the surface and the first image carrying device are carried. A first transfer means for transferring the toner image on the surface of the transfer material, a second transfer means for transferring the toner image carried by the second image carrying means on the back surface of the transfer material, and The first transfer means transfers the toner image carried by the first image carrying means onto the surface of the transfer material, and the second transfer means carries the toner image carried by the second image carrying means. An image forming apparatus having a fixing unit configured to transfer a toner image on the back surface of the transfer material and fix the toner images transferred on both surfaces of the transfer material, in the image forming apparatus. The material is the first image bearing means and the second image bearing means. Guide means for entering during provided,
When the transfer material enters between the first image carrying means and the second image carrying means, the leading end of the transfer material is brought into contact with the first image carrying means by the guide means. At the same time, the transfer material is charged to the same polarity as the toner,
This is achieved by an image forming apparatus characterized in that the image forming apparatus is brought into intimate contact with the image carrying means of (2).

[0009]

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

The photosensitive drum 10, which is an image bearing member, is provided with a cylindrical substrate formed of a transparent member such as optical glass or transparent acrylic resin 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.

The photosensitive drum 10 is sandwiched by a front flange 10a and a rear flange 10b, and the front flange 10a is bearing-supported by a guide pin 10P1 provided on a cover 103 attached to a front side plate 101 of the apparatus main body.
The rear flange 10b is fitted onto a plurality of guide rollers 10R attached to the rear side plate 102 of the main body of the apparatus to hold the photosensitive drum 10. A gear 10G provided on the outer periphery of the rear flange 10b is meshed with a driving gear G1, and the power of the gear 10G rotates the photosensitive drum 10 in a clockwise direction indicated by an arrow in FIG. 1 with the transparent conductive layer being grounded. It

In the present embodiment, it is sufficient that the photoconductive layer of the photosensitive drum has an exposure light amount capable of imparting an appropriate contrast. Therefore, the light transmittance of the transparent substrate of the photosensitive drum in the present embodiment does not need to be 100%, and may have a characteristic that some light is absorbed when the exposure beam is transmitted. As the material of the translucent substrate, an acrylic resin, particularly one polymerized using methyl methacrylate monomer, has transparency, strength, accuracy,
Acrylic, fluorine used for other general optical members, etc.
Various translucent resins such as polyester, polycarbonate, and polyethylene terephthalate can be used. Further, as long as it has a light-transmitting property with respect to the exposure light, it may be colored. For the transparent conductive layer, a vacuum deposition method, an active reaction deposition method, various sputtering methods, various CVs are used as a film forming method.
A thin film made of indium tin oxide (ITO), alumina, tin oxide, lead oxide, indium oxide, copper iodide, or Au, Ag, Ni, Al, etc., which maintains transparency, is used. Alternatively, a dip coating method, a spray coating method, or the like is used as the film forming method, and a conductive resin or the like made of the above metal fine particles and a binder resin is used. As the photoconductor layer, an amorphous silicon (a-Si) alloy photosensitive layer, an amorphous selenium alloy photosensitive layer, or various organic photosensitive layers (OPC) can be used.

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 exposure 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 development 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). Exposure for each color is performed on a cylindrical holding member 20 fixed with guide pins 10P2 provided on the rear plate 102 of the apparatus main body and guide pins 10P1 provided on the cover 103 attached to the front plate 101 as guides. Unit 12, uniform exposure device 1
2c and a transfer simultaneous exposure device 12d are attached and housed inside the substrate of the photoconductor drum 10. Image data of each color read by a separate image reading device and stored in the memory is sequentially read from the memory and input to the exposure unit 12 for each color as an electric signal.

As the exposure element, an element in which a plurality of light-emitting elements such as FL (phosphor light emission), EL (electroluminescence), PL (plasma discharge), and LED (light-emitting diode) are arranged in an array is 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 a 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 is
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, for example, a thickness of 0.5 to 1 mm that rotates in the same direction as the rotation direction of the photosensitive drum 10,
The developing sleeve 131 is formed of a cylindrical non-magnetic stainless steel or aluminum material having 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 to 1
Developing device 1 for each color which is kept in
In the developing operation by 3, the developing bias applied with the DC voltage or the AC voltage AC is applied to the developing sleeve 131, the jumping development is performed by the one-component or two-component developer accommodated in the developing device, and the developing sleeve 131 is transparent. A non-contact reversal development is performed in which a DC bias having the same polarity as the toner (negative polarity in the present embodiment) is applied to the negatively charged photosensitive drum 10 that grounds the conductive layer to attach the toner to the exposed portion. Be seen. 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 unit 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).

As a document image, 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 colors. And stored.

A gear 10 provided on the rear flange 10b of the photoconductor drum 10 is driven through a gear G1 for driving 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, the Y exposure unit 12 starts exposure with a first color signal, that is, an electric signal corresponding to Y image data, and the rotation of the drum scans the surface to expose the photosensitive drum 10. 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 yellow (Y) toner image, and further on the left side of the photosensitive drum 10 and above the yellow (Y), a magenta (M) developing device 1 is provided.
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 developing unit 13 for cyan (C) is located 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. In order to stabilize the temperature inside the photosensitive drum 10 and prevent the temperature from rising due to the heat generated by each exposure optical system 12, a material having good thermal conductivity is used for the holding member 20, and a heater 201 is used when the temperature is low. When the temperature is high, it can be suppressed to a level without any trouble by taking measures such as radiating heat to the outside through the heat pipe 202.

By the above-described image forming process, a superimposed color toner image serving as a back image is formed on the photosensitive drum 10 (first image carrying means) 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 photoconductive 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 photoconductive 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 is synchronized with the transfer area 14b, and the surface image of the superimposed color toner image is transferred to the photosensitive drum in the same manner as in the above-described color image forming process. 10 is formed. 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 a paper feed cassette 15 which is a transfer material storage means by a sending roller 15a, is fed by a feeding roller 15b, and is conveyed to a timing roller 15c.

The recording paper P is driven by the timing roller 15c to form a color toner image of a front image carried on the photosensitive drum 10 and a color toner image of a back image carried on the toner image receiver 14a. The paper is fed to the transfer area 14b in synchronization. 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 this 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 overlap each other, it is preferable that the upper and lower toner layers of the toner layer are charged to the same polarity with the same charge amount in order 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.

Repeated reversal development on the image carrier, the color toner images of the same polarity formed by superposition are collectively transferred to the toner image receiving body 14a without changing the polarity, and then the recording paper without changing the polarity. The batch transfer to P is preferable because it contributes to the improvement of transferability in the back side 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 image forming method for the front surface and the back surface. 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 receiving member 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 contacts and contacts 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 image deterioration is small. 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 bearing means or the second image bearing means.

A first example of transfer material feeding will be described with reference to FIGS. 4 and 5. FIG. 4 is a diagram showing how the transfer material enters the toner image receiving body, and FIG. 5 is a diagram showing the charging process of the transfer material charging means.

As shown in FIG. 4, the transfer area 14b on the transfer device 14c as the first transfer means serves as a nip portion so that the toner image of the surface image on the photosensitive drum 10 is transferred well. The toner image receiver 14a is the photosensitive drum 1.
It is preferable that the recording sheet P is formed in contact with 0, and further, an angle θ formed by the central axis of the photosensitive drum 10 and the half-value width of the nip portion is set so that the recording paper P as a transfer material can smoothly enter the nip portion. Is preferably from 15 to 14 °. The angle θ is 7.
If it is less than 5 °, good transfer is not achieved, and it is 14 °.
In the above case, bending or bending occurs when the transfer material enters.

The recording paper P comes into close contact with the toner image of the back side image on the toner image receiving body 14a on the driven roller 14e and passes through the transfer area 14b, and the back side transfer device 14 as the second transfer means.
Although it is conveyed to g, it is preferable that the distance between the contact area and the transfer area 14b is short because the toner image and the recording paper P are not displaced from each other. Therefore, the maximum image size, eg A
Drive roller 14d and driven roller 14e of toner image receiving body 14a having a peripheral length required to carry -3 size.
The distance L between the center axes of the rollers and the center L of the nip portion formed as the transfer area 14b.
3, the transfer area 14b is provided closer to the driven roller 14e side by L / 10 to 4L / 10, and the toner image receiving body 14 is provided.
a is arranged, and the interval to the transfer area 14b of the recording paper P which is closely contacted on the driven roller 14e is shortened.

The recording paper P is fed to the toner image receiver 14a on the driven roller 14e 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 P to come into close contact with the toner image of the back side image on the toner image receiving body 14a, the closer it comes to close without disturbing the toner image, so the leading edge of the recording paper P fed along the lower guide plate. Is brought into contact with the toner image receiving body 14a from the center of the driven roller 14e between the upstream side L2 and the downstream side L1 with respect to the feeding direction of the recording paper P, and the value of L1 is from 8 mm to 0, the value of L2 is 0
Is preferably 2 mm, and more preferably 5 mm to 0 as the value of L1. In addition, 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,
Further, when the angle is 20 ° or more, the toner image receiver 1 of the recording paper P is
4a is caught.

As described above, since the toner image of the surface image on the photosensitive drum 10 and the recording paper P are kept in non-contact with each other until just before the transfer area 14b, the toner image of the surface image is not disturbed and the recording paper P is not disturbed. They are combined and transferred onto the recording paper P by the transfer device 14c.

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 receiving body 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.

Further, as explained in the image forming process of FIGS. 1 to 3, the transfer device 14c as the first transfer means causes the toner image as the second image carrying means on the conveyed recording paper P. By applying a voltage having a polarity (plus polarity in this embodiment) different from that of the toner through the image receiving body 14a, the first
The toner image on the photosensitive drum 10 as the image carrying means is transferred onto the surface of the recording paper P as the transfer material, and then the surface of the recording paper P is transferred by the back surface transfer device 14g as the second transfer means. The toner image on the toner image receiving body 14a serving as the second image carrying unit is transferred to the back surface of the recording paper P by performing charging with a polarity (plus polarity in this embodiment) different from that of the toner to form a double-sided image. Done.

As described above, the recording paper is brought into good contact with the toner image receiving body, the toner is prevented from moving to the recording paper, and good double-sided transfer is performed.

A second example of feeding the transfer material will be described with reference to FIG. FIG. 6 is a diagram showing a method of introducing the transfer material into the photosensitive drum.

As described with reference to FIG. 4, the transfer area 14b on the transfer device 14c as the first transfer means is provided so that the toner image of the surface image on the photosensitive drum 10 is transferred well. It is preferable that the toner image receiving body 14a is formed as a nip portion in contact with the photoconductor drum 10, and further, the recording paper P as a transfer material is smoothly inserted into the nip portion. The angle θ between the center and the half width of the nip portion is preferably 7.5 to 14 °. 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 conveyed to the transfer area 14b in close contact with the toner image of the surface image on the photosensitive drum 10, but the toner image and the recording paper are shorter when the distance from the contact to the transfer area 14b is shorter. It is preferable because it is conveyed without any deviation from P. Therefore, the toner image receiving body 1 having a perimeter that is required to carry a rear surface image having a maximum image size, for example, A-3 size, which is formed in synchronization with the front surface image in the transfer area 14a.
4a, the distance L3 between the center of the driving roller 14d and the driven roller 14e is L / 10, and the distance L3 between the intermediate position of both rollers and the center of the nip formed as the transfer area 14b is L / 10.
The transfer area 14b is provided closer to the driven roller 14e side by about 4 L / 10, the toner image receiving body 14a is arranged, and the interval to the transfer area 14b of the recording paper P closely contacted on the driven roller 14e is shortened. To do.

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.
The position where the front end of the recording paper P fed along 51a abuts on the photoconductor drum 10 is the vertical line passing through the central axis of the photoconductor drum 10 and the contact portion of the recording paper P on the photoconductor drum 10. Is an angle α1, the guide portion 151 of the lower guide plate 151
The upper surface of the recording paper P fed along with a and the photosensitive drum 1
When the angle formed by the contact portion of the recording paper P with 0 is α2,
The angle α1 is preferably 28 to 32 °, and the angle α2 with respect to the angle α1 is preferably 57 to 53 °. When the angle α1 is 28 ° or less and the angle α2 is 57 ° or more, the recording paper P and the photosensitive drum 10 are
The adhesion with is not good, and the angle α1 is 32 ° or more,
When the angle α2 is 53 ° or less, the recording paper P is caught on the photosensitive drum 10. In addition, the lower guide plate 151
Between the bent portion 151c and the peripheral surface of the photosensitive drum 10
4 is 0.5 to 2 mm, and the length L5 of the bent portion 151b is 3 to
The thickness of 5 mm is preferable because the recording paper P can be smoothly entered.

As described above, the toner image of the back side image on the toner image receiving body 14a and the recording paper P are kept in non-contact until just before the nip portion as the transfer area 14b, so that the toner image of the back side image is not disturbed. The transfer device 14c with the recording paper P
The image is transferred onto the recording paper P by the back surface transfer device 14g through the transfer area 14b on the upper side.

In the same manner as described with reference to FIG. 5, the recording paper P
When the image is aligned with the front edge of the surface image and enters the photoconductor drum 10, a bias voltage of −500 to −2 kVDC of the same polarity as the toner (negative polarity in this embodiment) is applied to the lower guide plate 151 as a transfer material charging unit. E2 is preferably applied, and the bias voltage E2 during passage of the recording paper P is applied.
Is continuously applied, 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. 5, the toner (minus polarity) is not attracted to the recording paper P as described with reference to FIG. 5, and the image is disturbed due to the toner movement particularly when the recording paper P is made to have the positive polarity. There is no. 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.

Further, as explained in the image forming process of FIGS. 1 to 3, the transfer device 14c as the first transfer means transfers the toner image as the second image carrying means to the conveyed recording paper P. By applying a voltage having a polarity (plus polarity in this embodiment) different from that of the toner through the image receiving body 14a, the first
The toner image on the photosensitive drum 10 as the image carrying means is transferred onto the surface of the recording paper P as the transfer material, and then the surface of the recording paper P is transferred by the back surface transfer device 14g as the second transfer means. The toner image on the toner image receiving body 14a serving as the second image carrying unit is transferred to the back surface of the recording paper P by performing charging with a polarity (plus polarity in this embodiment) different from that of the toner to form a double-sided image. Done.

By the 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.
No. 28740, which reverses the toner polarity corresponding to the back side image, and simultaneously transfers to both surfaces of the transfer material,
JP-A-63-180969, JP-A-63-29825
No. 5, Japanese Patent Laid-Open No. 1-44457, and other tandem systems,
The fact that the process conditions and the image data processing conditions as described above are changed between the front surface and the back surface is used, and it is possible to form a double-sided image having a uniform image density and color tone.

[0063]

According to the first aspect, one side of the transfer material is the second side.
Of the toner image on the second image carrier means, the toner image on the first image carrier means is prevented, and the toner image on the first image carrier means is prevented. The good transfer is performed on both surfaces of the transfer material without disturbing the toner image.

According to the second 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. The transfer of toner 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 showing 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 showing a problem of the related art.

[Explanation of symbols]

 10 Photoconductor drum 11 Scorotron charger 12 Exposure unit 13 Developer 14a Toner image receiver 14b Transfer area 14c Transfer device 14d Driving roller 14e Driven roller 14g Backside transfer device 17 Fixing device 51, 151 Lower guide plate 52, 152 Upper guide plate E1, E2 Bias voltage P Recording paper

Claims (2)

[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 transfer material is placed near the first image carrier and the first transfer medium is placed on the transfer material.
Guide means for advancing between the first image carrying means and the second image carrying means is provided, and when the transfer material enters between the first image carrying means and the second image carrying means. The guide means causes the leading end of the transfer material to come into contact with the second image carrying means first, and the transfer material is charged to the same polarity as the toner,
An image forming apparatus, which is brought into close contact with the image carrying means of 1. 2. 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 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 to the back surface of the transfer material by the second transfer means, and the toner image carried on the back surface of the transfer material, In an image forming apparatus having a fixing unit for fixing The transfer material is moved to the first image carrier means in the vicinity of the first image carrier means.
Guide means for advancing between the first image carrying means and the second image carrying means is provided, and when the transfer material enters between the first image carrying means and the second image carrying means. The guide means causes the leading edge of the transfer material to come into contact with the first image bearing means first, and the transfer material is charged to the same polarity as the toner,
An image forming apparatus characterized in that the image forming apparatus is brought into intimate contact with the image carrying means.