JPH11119475A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of preventing an image from being irregular and capable of forming a double-sided image hardly causing error such as a jamming with a mechanically simple constitution. SOLUTION: In the first image forming section 5, the toner image consisting of toner particles (+) charged in positive electric charge is transferred onto an intermediate transfer belt 33 charged in negative electric charge. Next, the toner image consisting of the toner particles (+) is transferred onto a surface of paper 15 by a secondary transfer roller 37 charged in the same positive electric charge. In the second image forming section 7, the toner image consisting of the toner particles (+) is transferred onto the intermediate transfer belt 33' charged in the negative electric charge. Subsequently, the toner particles (+) charged in the positive electric charge are reversed to the negative electric charge (-) by an inversion charger 45. Thereafter, the toner image consisting of the toner particles (+), is transferred onto the rear side of the paper 15 by the secondary transfer roller 37' charged in the same negative electric charge. Therefore, the image is prevented from being irregular by repulsion, since potential of the toner image on the front/rear side of the paper 15 is respectively reversed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printer or a copier having the ability to print on both sides of an output medium, and more particularly to an image forming apparatus such as a multicolor printer or a copier.

[0002]

2. Description of the Related Art In recent years, it has been desired that an image forming apparatus (also referred to as an image forming apparatus), particularly a color image forming apparatus, have an output function for both sides of paper. In a conventional image forming apparatus, there is provided a reversing sheet feeding mechanism for forming an image on one side, reversing and fixing the sheet after fixing, feeding the sheet again, and reversing the fixed sheet after forming an image (imaging) on one side. Double-sided output is realized by feeding paper to the image forming unit again by the paper feeding mechanism.

[0003]

However, the reversing sheet feeding mechanism is complicated and may cause a trouble such as a jam or a failure in the sheet feeding mechanism. Also, it is a limiting factor for the paper type and the number of images to be formed.

Therefore, it is conceivable to provide a plurality of image forming means and simultaneously or continuously form images on both sides of the paper to achieve double-sided output. However, when the electrophotographic image forming means having the same configuration is used here, the image before fixing processing formed on one surface disturbs the image formation (image formation) on the other surface due to repulsion. However, the image cannot be neutralized before fixing because the image adheres to the paper due to the charging. Further, since the image before the fixing process is merely attached by the electrostatic force, the image is easily disturbed by mechanical contact, so that the conveyance means is limited.

On the other hand, JP-A-7-77851 discloses that
Electrophotographic single-path multi-station printer for double-sided printing, which is a double-sided printing means for continuous paper and has a mechanism for alternately forming images on the front and back sides and changing the charging of a toner image on an output medium during the formation. Is disclosed. However, in this apparatus, since the image forming means for forming an image on the front surface and the back surface charges the toner particles with mutually opposite potentials, it is necessary to prepare image forming means having different structures.
The overall structure is also complicated.

According to the present invention, it is possible to prevent image distortion.
It is an object of the present invention to provide an image forming apparatus capable of forming a double-sided image with a mechanically simple configuration and in which an error such as a jam is unlikely to occur.

[0007]

According to one aspect of the present invention, there is provided a medium supply unit for supplying an output medium, and an image formed on a surface of the output medium supplied from the medium supply unit. A first image forming unit to be created, a second image forming unit disposed at a position symmetrical to the first image forming unit with respect to the output medium, and forming an image on the back surface of the output medium; An image fixing unit for fixing an image, wherein the first image forming unit and the second image forming unit form toner images of the same polarity, and the first image forming unit or the Either of the two image forming units has a charge reversing means for reversing the charge polarity of the toner image before transferring to the output medium.

According to the first aspect of the present invention, the first
And one of the second image forming units has a charge reversing means for reversing the charge polarity of the toner image before transferring to the output medium, so that the potentials of the toner images transferred to the front and back surfaces of the output medium are opposite to each other. It is at a potential, and there is no possibility that the toner images are disturbed by repulsion.

According to a second aspect of the present invention, in the first aspect, the moving direction of the output medium after transferring the toner images in the first image forming unit and the second image forming unit is vertically downward. And providing an image fixing unit on an extension of the moving direction, so that the output medium, on which images are formed on both surfaces in the first image forming unit and the second image forming unit, is brought into contact with another member. And supplying the image to the image fixing unit.

According to the second aspect of the present invention, the moving direction of the output medium during image formation (hereinafter referred to as the image forming direction) is vertically downward, and the image fixing unit is extended on the extension thereof. With this arrangement, the output medium having the image formed on the front and back surfaces can be introduced into the image fixing unit without using a support mechanism that contacts the output medium. Therefore, the image is prevented from being disturbed by the support mechanism. Further, since the gravity is parallel to the image forming direction, it is possible to make almost no difference in the configuration between the first image forming unit and the second image forming unit.

According to a third aspect of the present invention, there is provided a medium supply section for supplying an output medium, a first image forming section for forming an image on a surface of the output medium supplied from the medium supply section, and a first image forming section for the output medium. Image formation comprising: a second image forming unit disposed at a position symmetrical to the image forming unit and forming an image on the back surface of the output medium; and an image fixing unit fixing the images formed on the front and back surfaces of the output medium. In the apparatus, the first image forming unit and the second image forming unit are sublimation-type thermal transfer image forming units that transfer dye carriers having the same polarity to an output medium, and the dye images are set to potentials opposite to each other before transfer. The image forming apparatus further comprises a charging unit for charging, and a discharging unit for removing the charge of the output medium on which the dye image has been transferred before the image fixing unit.

According to the third aspect of the present invention, the first
And the second image forming unit has a charging unit for charging the dye carrier to a potential opposite to each other before transfer, so that the potentials of the dye images transferred to the front surface and the back surface of the output medium are opposite to each other. There is no fear of disturbing the image by repulsion. The potential of the output medium on which the dye image has been transferred is
The charge is eliminated by the charge eliminating means provided in the preceding stage of the image fixing section.

According to a fourth aspect of the present invention, in the third aspect of the present invention, the moving direction of the output medium at the time of image formation in the first image forming section and the second image forming section is vertically downward. And by providing an image fixing unit on the extension of the moving direction, the first image forming unit and the second
The image forming unit supplies the output medium, on which images are formed on both sides, to the image fixing unit without contacting other members.

According to the fourth aspect of the present invention, the image forming direction at the time of image formation is vertically downward and the image fixing section is provided on an extension of the image forming direction. The formed output medium can be introduced into the image fixing unit without using a support mechanism that contacts the output medium. Therefore, the image is prevented from being disturbed by the support mechanism. Further, since the gravity is parallel to the image forming direction, it is possible to make almost no difference in the configuration between the first image forming unit and the second image forming unit.

[0015]

Embodiments of the present invention will be described below in detail with reference to FIGS.

FIG. 1 is a duplex printing apparatus according to a first embodiment to which the image forming apparatus of the present invention shown in FIG. 1 is applied. This apparatus utilizes electrophotographic image forming means for image formation.

The double-sided printing apparatus 1 includes a paper feed unit 3, a first image forming (image forming) unit 5, a second image forming unit 7, an image fixing unit 9, and a post-processing unit 11.

The paper supply section 3 is provided with a guide roller 17 and a pair of guide rollers 19 to feed a paper 15 as an output medium stored in a paper supply cassette 13 to first and second papers disposed below the paper supply section 3. The power is supplied to the image forming units 5 and 7.

The first image forming section 5 has a cylindrical photosensitive member 21 as a photosensitive member. Along the outer periphery of the photoconductor 21, a primary charging charger 23 for charging the surface of the photoconductor 21 with a negative charge, and a negative charge corresponding to an image by exposing the surface of the photoconductor 21 to selectively dissipate the charge. An exposure device 25 for forming a charge distribution; a developing device 27 for charging toner particles with a positive charge and attracting the surface of the photoreceptor 21 by electrostatic force to form a toner image;
Primary charge removing charger 29 for removing the charge of
And a photoreceptor creep 31 for removing remaining toner particles attached to the surface of the photoreceptor.

The first image forming section 5 includes a primary transfer roller 35 provided along the outer periphery of the photoconductor 21 after the developing device 27 and before the primary charge removing charger 29, and a paper 1.
5, a secondary transfer roller 37 provided along the transport path 5, an intermediate transfer belt 33 extending between the rollers, and a secondary charging charger 39 for negatively charging the intermediate transfer belt 33. Therefore, after the intermediate transfer belt 33 is negatively charged by the secondary charging charger 39, the toner image charged with the positive charge on the surface of the photoconductor 21 between the photoconductor 21 and the primary transfer roller 35 is formed on the surface thereof. To the intermediate transfer belt 33
Then, the toner image is transferred to the surface of the paper 15 by a secondary transfer roller 37 charged with a positive charge. Further, the intermediate transfer belt 3 after the transfer of the toner image
And a belt cleaner 43 for removing remaining toner particles.

The second image forming section 7 is disposed symmetrically with respect to the paper 15 on which the toner image is to be transferred, and corrects the charge of the toner image transferred from the photoreceptor 21 onto the surface of the intermediate transfer belt 33. The configuration is the same as that of the first image forming unit 5 except that a reversing charger 45 for reversing the image from the negative to the negative is provided. That is, the second image forming unit 7 includes the photoconductor 21 ′, the primary charging charger 23 ′, the exposure device 25 ′, and the developing device 2
7 ', primary neutralization charger 29', photoconductor creep 3
1 ′, an intermediate transfer belt 33 ′, a primary transfer roller 35 ′,
A secondary transfer roller 37 ', an intermediate transfer belt 33', a secondary charging charger 39 ', a secondary discharging charger 41', and a belt cleaner 43 'are provided.

For the first image forming section 5 and the second image forming section 7 having such a configuration, the paper 15 fed from the paper feeding section 3 is fed to a paper provided immediately below the exit of the paper feeding section 3. Conveyor belt 5
1 and 53, the two secondary transfer rollers 37,
37 '. Therefore, the moving direction of the paper 15, that is, the image forming direction here is directed downward in the vertical direction.

First image forming section 5 and second image forming section 7
, That is, on the extension of the image forming direction, an image fixing unit 9 is provided. The image fixing unit 9 fixes the toner images transferred to the front and back surfaces of the paper 15. Immediately below the image fixing unit 9, a post-processing unit 11 for organizing and storing the paper 15 after fixing the image is provided.

A double-sided printing process in the double-sided printing apparatus 1 according to the first embodiment having the above configuration will be described with reference to FIG.

The first image forming section 5 transfers the toner image formed on the surface of the photoreceptor 21 and composed of positively charged toner particles (+) to the negatively charged intermediate transfer belt 33. Next, the toner image composed of the toner particles (+) is transferred to the paper 1 by a secondary transfer roller 37 charged to the same positive charge.
Transfer to the surface of No. 5.

On the other hand, the second image forming section 7 also
The toner image formed of the positively charged toner particles (+) formed on the surface of 1 ′ is transferred to the negatively charged intermediate transfer belt 33 ′. Next, the reversing charger 45
, The toner particles (+) charged to a positive charge are inverted to a negative charge (−). Thereafter, the toner image composed of the toner particles (+) is transferred to the back surface of the paper 15 by the secondary transfer roller 37 'charged to the same negative charge.

As described above, by providing the reversing charger 45 in the second image forming unit 7 and reversing the charge of the toner particles from positive to negative, the potential of the toner image transferred to the front and back surfaces of the paper 15 is reversed. With the help of the electric field formed by the secondary transfer rollers 37 and 37 ′, the image can be formed on the front and back surfaces of the paper 15 without disturbing the image due to repulsion.

Further, the duplex printing apparatus 1 according to the first embodiment
In the first embodiment, the moving direction (image forming direction) of the paper 15 in forming an image in the first image forming unit 5 and the second image forming unit 7 is downward in the vertical direction, and is extended in the image forming direction. Since the image fixing unit 9 is provided, the paper 1 on which images are formed on both sides
5 can be supplied to the image fixing unit 9 without contacting other members. As a result, as shown in FIG. 4, the image forming section 67 having the intermediate transfer belt 61, the secondary transfer roller 63 and the secondary transfer charger 65 is moved from the image forming section 67 having the upper fixing roller 71 and the lower fixing roller 73. 75, paper 1
It is not necessary to provide a transport mechanism such as a paper transport belt 77 that transports the sheet 5 and eliminates mechanical contact with the image before fixing.
Image disturbance can be reduced.

Further, since the image forming direction is parallel to the gravity, it is possible to almost eliminate the difference between the configurations of the first image forming section 5 and the second image forming section 7.

Further, the first image forming unit 5 and the second image forming unit 7 are made of the same material that charges toner particles at the same potential, and the second image forming unit 7 is provided with a reverse rotation charger 45. It is possible to form a clear image on the front and back surfaces of the 15 surfaces.

In the first embodiment, the paper 1
5. The potentials of the secondary transfer rollers 37 and 37 'may be completely opposite. That is, the + and-symbols shown in FIG. 2 do not directly represent a sign, but rather represent a relative potential relationship. The actual sign is determined by the configuration of the first and second image forming units 5 and 7.

Next, a two-sided printing apparatus according to a second embodiment will be described with reference to FIG. This apparatus differs from the double-sided printing apparatus 1 according to the first embodiment in that a sublimation type thermal transfer image forming unit that transfers a dye image to paper is used for image formation.

As shown in FIG. 3, in the double-sided printing apparatus 81, the first image forming section 83 uses the first dye carrier 8 before transfer.
The first charged charger 87 that charges the dye image on the surface of the surface 5 with a positive charge is provided immediately above the guide roller 89. The first dye carrier 85 is introduced into a first thermal transfer head 91 having a positive charge, and after thermally transferring the dye image to the paper 103, the first dye carrier 85 is fed back via a guide roller 93.

On the other hand, in the first image forming section 95, a second charged charger 99 for charging the dye image on the surface of the second dye carrier 97 before transfer with a negative charge is provided directly above the guide roller 101. The second dye carrier 97 is introduced into the second thermal transfer head 105 having a negative charge, which is located on the target with the paper 103 interposed between the thermal transfer head 91 and the dye image is thermally transferred to the paper 105, and then the guide is formed. The sheet is sent back via the roller 107. Further, the image fixing unit 109
Of the paper 105 at the entrance of the
Is provided.

The double-sided printing apparatus 81 having such a configuration
Then, before the transfer, the first dye carrier 85 and the second dye carrier 9
Since the first charging charger 87 and the second charging charger 99 for charging the sheet 7 to opposite potentials are provided, the potential of the dye image transferred to the front and back surfaces of the paper 103 is inverted by these, and the first thermal transfer is performed. With the help of the electric field constituted by the head 1 and the second thermal transfer head 2, the image can be transferred onto the paper 103 without disturbing the image by repulsion.

In the second embodiment, the paper 10
3. The potentials of the secondary transfer rollers 89 and 101, the first and second thermal transfer heads 91 and 105, and the like may be completely opposite. That is, the + and-symbols shown in FIG. 3 do not directly represent a sign, but rather represent a relative potential relationship. The actual positive / negative is determined by the first and second image forming means 8.
3, 95.

The present invention is not limited to the above embodiment,
Various changes can be made without departing from the spirit of the present invention. In the duplex printing apparatus 1 according to the first embodiment, the second image forming unit 7 that forms an image on the back surface of the paper 15 has the reverse charger 4.
5 is provided, but may be provided in the first image forming unit 5 that forms an image on the surface of the paper 15.

In the first and second embodiments, the case where the present invention is applied to a two-sided printing apparatus has been described.
The present invention is also applicable to an image forming apparatus as an output device of a copying machine.

[0039]

As described above, according to the first aspect of the present invention, the charge of the toner image is inverted before transferring to the output medium on one of the first and second image forming units. Since the charge reversal means is provided, it is possible to prevent the toner images formed on both surfaces of the output medium from being disturbed by repulsion, and to provide a mechanically simple configuration by combining the first and second image forming units having the same configuration. Double-sided image formation can be performed.

According to the second aspect of the present invention, since the image forming direction at the time of image formation is vertically downward and the image fixing section is provided on the extension thereof, the support for contacting the output medium is provided. By eliminating the mechanism, it is possible to prevent the occurrence of image disorder due to the support mechanism.

According to the third aspect of the present invention, since the first and second image forming units each have a charging unit for charging the dye carrier to the opposite potential before the transfer, the first and second image forming units are formed on both surfaces of the output medium. The dye image can be prevented from being disturbed by repulsion, and the combination of the first and second image forming units having the same configuration can perform double-sided image formation with a mechanically simple configuration.

According to the fourth aspect of the present invention, since the image forming direction at the time of image formation is vertically downward and the image fixing section is provided on the extension thereof, the support for contacting the output medium is provided. The mechanism can be eliminated, and the occurrence of image disturbance due to the support mechanism can be prevented.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating an entire configuration of a two-sided printing apparatus according to a first embodiment of the present invention.

FIG. 2 is a schematic diagram illustrating a main part of the duplex printing apparatus according to the first embodiment of the present invention.

FIG. 3 is a schematic diagram illustrating a main part of a duplex printing apparatus according to a second embodiment of the present invention.

FIG. 4 is a schematic view showing a horizontal transport mechanism as a reference example.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 Double-sided printing device 3 Paper feed unit 5 First image forming unit 7 Second image forming unit 11 Post-processing unit 15 Paper 33, 33 ′ Intermediate transfer belt 37, 37 ′ Secondary transfer roller 45 Reverse charger 83 First image forming unit 85 first dye carrier 87 first charged charger 95 second image forming unit 97 second dye carrier 99 first charged charger 111 static elimination means

Claims (4)

[Claims] 1. A medium supply section for supplying an output medium, a first image forming section for forming an image on a surface of the output medium supplied from the medium supply section, and a position symmetrical to the first image forming section with respect to the output medium. A second image forming unit disposed on the output medium and forming an image on the back surface of the output medium; and an image fixing unit fixing the images formed on the front and back surfaces of the output medium. The forming unit and the second image forming unit form toner images of the same polarity, and one of the first image forming unit and the second image forming unit forms a toner image before transferring the toner image to the output medium. An image forming apparatus comprising a charge reversing unit for reversing a charging polarity. 2. The method according to claim 1, wherein the moving direction of the output medium after transferring the toner image in the first image forming unit and the second image forming unit is vertically downward, and the image fixing unit is provided on an extension of the moving direction. And supplying the output medium, on which images are formed on both sides in the first image forming unit and the second image forming unit, to the image fixing unit without contacting another member. An image forming apparatus according to claim 1. 3. A medium supply unit for supplying an output medium, a first image forming unit for forming an image on a surface of the output medium supplied from the medium supply unit, and a position symmetrical to the first image forming unit with respect to the output medium. And a second image forming unit for forming an image on the back surface of the output medium, and an image fixing unit for fixing the image formed on the front and back surfaces of the output medium. And the second image forming unit are sublimation type thermal transfer type image forming units for transferring dye carriers of the same polarity to an output medium, and have charging units for charging the dye images to opposite potentials before transfer. An image forming apparatus further comprising a charge eliminator for removing the charge of the output medium having the dye image transferred thereon before the image fixing unit. 4. The image forming apparatus according to claim 1, wherein the moving direction of the output medium at the time of image formation in the first image forming unit and the second image forming unit is vertically downward, and an image fixing unit is provided on an extension of the moving direction. And supplying the output medium, on which images are formed on both sides in the first image forming unit and the second image forming unit, to the image fixing unit without contacting other members. An image forming apparatus according to claim 1.