JPH06149002A - Image forming device - Google Patents

Abstract

PURPOSE:To improve a maintenance performance by restraining a voltage from boosting at a multiple transfer time, attaining the use of a high-resistance thick dielectric sheet-like recording material carrying means and also eliminating the remaining charge of the recording material carrying means at the reverse electrifying time. CONSTITUTION:The constant voltage of -4kV is impressed on an inside belt destaticizer which is in contact with the inside of a recording material carrying belt from the time of preliminarily electrifying until a 4th color image is formed, and the recording material carrying belt is electrified so as to have a polarity which is reverse to that of a transfer voltage. Also, at a post-rotation process after a final printed image is outputted, the voltage of -2kV is impressed on the inside belt destaticizer so that the surface potential of the recording material carrying belt goes to zero V within a voltage lower than the voltage at the reverse electrifying time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic system, in which a visible image is formed on an image bearing member, and the visible image is transferred to a recording material which is carried and conveyed by a recording material carrying means. With respect to an image forming apparatus such as an electrographic recording method, for example, but not limited to, a visible image of a plurality of different colors is formed on an image carrier, and these visible images are carried and conveyed by a recording material carrying means. The present invention is suitable for a color image forming apparatus such as a color copying machine or a color printer, which is configured so as to be successively transferred onto the same recording material.

[0002]

2. Description of the Related Art Conventionally, an image forming apparatus having a plurality of image forming sections, forming toner images of different colors in each image forming section, and successively transferring these toner images onto the same recording material, Various so-called color image forming apparatuses have been proposed. Among them, the electrophotographic color image forming apparatus is widely used. As this electrophotographic color image forming apparatus, for example, a plurality of image forming units, generally four image forming units are arranged side by side, and respective dedicated photoconductor drums are used as image carriers of these image forming units. Cyan, magenta, yellow, and black visible images, that is, toner images are separately formed on the drum, and are sequentially recorded on the recording material that is carried and conveyed by the recording material carrying means such as a dielectric belt. There is a configuration in which a required full-color image or a multi-color image is obtained by superposing and transferring toner images and collectively heating and fixing the multiple toner images on the recording material by a fixing device.

An example of such an electrophotographic color image forming apparatus, a color copying machine in this example, will be briefly described with reference to FIG. This color copying machine has a structure in which four image forming sections Pa, Pb, Pc and Pd are linearly arranged in the main body of the apparatus, and each of the image forming sections Pa to Pd is a dedicated photosensitive member as an image carrier. Body drums 1a, 1b, 1c
And 1d respectively, and each of the photosensitive drums 1a to 1d is surrounded by a dedicated latent image forming section, developing section, transfer section,
A cleaning unit and the like are provided.

The latent image forming section includes photoconductor drums 1a-1a.
exposure lamps 21a, 21b, 21 arranged on the outer periphery of d
c and 21d, drum chargers 2a, 2b, 2c and 2d that uniformly charge the photoconductor drums 1a to 1d, a polygon mirror 17 for scanning light emitted from a light source device (not shown), and a photoconductor. Potential sensors 22a, 22b, 22c and 2 for detecting the surface potential of the drums 1a to 1d.
2d, the laser beam emitted from the light source device, for example, is scanned by rotating the polygon mirror 17, and the scanning light obtained by deflecting the light beam by the reflection mirror is collected on the generatrix of the photoconductor drums 1a to 1d. A latent image corresponding to an image signal is formed via the fθ lens that emits light.

Further, the developing section includes developing units 3a, 3b, 3
c and 3d, the developing device 3a contains a cyan (hereinafter abbreviated as C) color developer, the developing device 3b contains a magenta (hereinafter abbreviated as M) color developer, and the developing device 3c contains Is a yellow (hereinafter abbreviated as Y) color developer, and the developing device 3d is filled with a black (hereinafter abbreviated as K) color developer by a predetermined amount by a developer supply device (not shown). . These developing devices 3a to 3d attach a developer to the latent images of C, M, Y, and K formed on the photoconductor drums 1a to 1d to attach C, M, Y, and C on the photoconductor drums 1a to 1d.
Each of the K visible images is formed.

In addition, the transfer section includes the image forming sections Pa to
The drive roller 1 is provided below the Pd photosensitive drums 1a to 1d.
0 and a pair of driven rollers 11a and 11b, an endless recording material carrying means arranged in a stretched state, in this example, an endless recording material carrying belt 8, and inside the recording material carrying belt 8. A pair of registration rollers 13 from a sheet feeding device including a recording material cassette 60 that contains the recording material 6 and that includes the arranged corotron or conductive rollers and brush-shaped transfer means 4a, 4b, 4c and 4d. , 13 hold the recording material 6 fed at a timing by the recording material carrying belt 8 and sequentially convey it to the image forming portions Pa to Pd, and the transfer means 4a to 4d apply an electric field or electric charge. C formed on each of the photosensitive drums 1a to 1d by
The visible images of M, Y, and K are transferred onto the recording material 6 in an overlapping manner.

Here, the recording material carrying belt 8 includes a polyethylene terephthalate resin film sheet (PET sheet), a polyvinylidene fluoride resin film sheet,
It is a film of a dielectric resin such as a polyurethane resin film sheet, and both ends thereof are overlapped and joined to each other to form an endless shape, or a seamless (seamless) belt is used. In the case of a belt having no seams, it is not only difficult to manufacture a belt having uniform physical properties, but also a belt having a stable circumference and mass production such as manufacturing time are not suitable in terms of cost and the like. On the other hand, in the case of a belt having a seam, when the image is formed at the seam position, the unevenness of the seam and the change of the physical properties such as the resistance value cannot be avoided, and the image is disturbed when the image is formed on the seam. Therefore, in order to obtain a high-quality image, it is general to provide a means for detecting a seam position (not shown) so as not to form an image on the seam.

When the recording material carrying belt 8 starts moving, the recording material 6 is fed from the registration roller 13 onto the recording material carrying belt 8. At this time, the image writing signal is turned on, and the visible image of C color is formed on the photosensitive drum 1a of the first image forming portion Pa at a certain timing. Then, when the recording material 6 reaches the lower side of the photosensitive drum 1a, a corotron, or a conductive roller or a brush-shaped transfer unit 4a gives an electric field or an electric charge, so that the visible light on the photosensitive drum 1a is visible. The image is transferred onto the recording material 6. At this time, the recording material 6 is held by the electrostatic attraction force on the recording material carrying belt 8 and is conveyed to the second image forming portion Pb.

As described above, while the C color visible image is being transferred onto the recording material 6 in the first image forming portion Pa, the M component color electrostatic latent image is formed in the second image forming portion Pb. The electrostatic latent image is made into a visible image of M color by the developing device 3b, and when the recording material 6 is conveyed to the transfer area below the photosensitive drum 1b of the second image forming portion Pb, this M color image is transferred. Is transferred to the transfer area, and is transferred in the state of being superimposed on the C color visible image on the recording material 6 by the same action of the transfer means 4b.

Hereinafter, the third and fourth image forming portions Pc and Pd will be described.
In the case of Y, as in the first and second image forming portions Pa and Pb,
The visible images of colors K and K are sequentially formed, and are transferred onto the recording material 6 conveyed by the recording material carrying belt 8 on the transfer means 4c,
By the action of 4d, these visible images are sequentially transferred in multiple.

When the image forming process is completed, the recording material 6 is destaticized by the action of the separation charging device 14 and the peeling charging device 15, and is separated from the recording material carrying belt 8 by the attenuation of the electrostatic adsorption force, and the fixing portion 7 is formed. The desired full-color image is obtained by being transported to and fixed in one batch.

The fixing unit 7 includes a fixing roller 71 and a pressure roller 72, heat-resistant cleaning members 73 and 74 for cleaning the rollers 71 and 72, and heaters 75 and 7 for heating the rollers 71 and 72, respectively.
6, an oil application roller 77 for applying a release agent oil such as dimethyl silicone to the fixing roller 71, an oil reservoir 78 for supplying the oil, and a thermistor 79 for controlling the fixing temperature.

On the other hand, each of the image forming portions Pa to
The Pd photosensitive drums 1a to 1d are cleaning units 5a,
The residual contaminants such as the developer are removed by 5b, 5c and 5d to prepare for the subsequent latent image formation. In addition, a contaminant such as a developer remaining on the recording material carrying belt 8 is a pair of belt static eliminators (charge eliminators for static elimination) which are arranged inside and outside so as to sandwich the recording material carrying belt 8 therebetween.
After the electricity is removed by 12a and 12b to remove the electrostatic attraction force, it is scraped off by the transfer cleaning device 9 having the rotating fur brush 16. As the cleaning member of the transfer cleaning device 9, a blade or a non-woven fabric, or a combination thereof may be used in addition to the fur brush.

In the image forming apparatus having the above structure, when the recording material carrying belt 8 is destaticized, the separation charging device 14 and the peeling charging device 15 form a pair, and the insides of the recording material carrying belt 8 are opposed to each other. And outer belt static eliminators 12a and 1
2b form a pair, and an alternating voltage of a sine wave or a rectangular wave having a phase difference of 180 degrees with respect to the chargers 14 and 15 and the static eliminators 12a and 12b forming the pair, and the maximum amplitude is 10
Generally, a voltage of about 15 KV and a frequency of about 500 Hz is often applied, but in some cases, a DC voltage having a polarity opposite to the potential applied to the recording material carrying belt 8 at the time of transfer is applied, or AC and DC are applied. In some cases, a voltage in which is superimposed is applied. These static elimination voltages are applied so as to remove the residual charges on the recording material carrying belt 8.

[0015]

However, in order to efficiently remove the residual charge of the recording material carrying means, it has been necessary to apply an alternating current having a large amplitude in the charge removal of the recording material carrying means. On the other hand, when the potential on the recording material carrying means is charged to the same polarity as the potential applied at the time of transfer by the charge eliminating means in order to remove the residual charge,
In a multi-transfer type apparatus in which the potentials are successively increased, the required high voltage output becomes large, and there is a drawback that various obstacles such as cost increase and discharge occur.

On the other hand, as disclosed in Japanese Unexamined Patent Publication No. 51-157626, in order to remove the residual charge, the electric charge on the recording material carrying means is charged to the opposite polarity to the electric potential applied at the time of transfer by the charge removing means. In this case, the charge on the recording material carrying means charges the image carrier when the apparatus is in a standing state, and this becomes a residual charge even at the time of subsequent recording, and the charge is perpendicular to the main scanning direction (perpendicular to the recording material conveying direction). Image defects such as line-shaped density unevenness occur in the direction). Further, there are drawbacks such as electrostatically sticking to the apparatus main body or the like when exchanging or maintaining the recording material carrying means, or causing discomfort due to static electricity when touched with a hand or the like.

Therefore, an object of the present invention is to suppress the voltage rise at the time of multiple transfer so that the high voltage output required for transfer can be reduced, and at the same time, a dielectric having a high resistance of 10 ¹⁵ Ω · cm or more can be used. A thick film or sheet can be used as the recording material carrying means, and the reverse charging sequence can be controlled so as to eliminate the residual charge when the recording material carrying means is reversely charged. An object of the present invention is to provide an image forming apparatus with improved maintainability such as replacement of means.

[0018]

The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention comprises an image carrier on which a latent image is formed, a developing means for developing the latent image on the image carrier to form a visible image, and a recording material to which the visible image is transferred. A recording material carrying means for carrying the recording material carrying means to the transfer position of the image carrier, and transferring the visible image to the recording material via the recording material carrying means at the transfer position or to the recording material carrying means. An image forming apparatus provided with a decharging means for equalizing the potential on the recording material carrying means before the transfer operation of the visible image, the decharging means comprising:
During the image forming operation for outputting a print image, the electric potential on the recording material holding means is controlled to be the reverse electric potential during the transfer operation, and the electric potential on the recording material holding means is changed except during the image forming operation. The image forming apparatus is characterized in that the main body of the apparatus is controlled to be zero.

[0019]

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

Since the first embodiment of the present invention is applied to the electrophotographic color copying machine shown in FIG. 5, a description of the structure and operation of the color copying machine will be given. Although omitted unless necessary, the present invention is equally applicable to image forming apparatuses of various configurations other than the embodiment, such as an electrophotographic system and an electrostatic recording system.

FIG. 1 is a timing chart showing a sequence of a typical control operation according to the first embodiment of the present invention.
6 shows a case where two color print images are continuously output by the electrophotographic color copying machine shown in FIG. “Preliminary charging” on the horizontal axis, which is the time axis t, is an operation of equalizing the electric potential of the recording material carrying belt 8 so that image output can be performed stably, and during this time, the recording material 6 in the cassette 60 is provided. Is conveyed to the registration roller 13. Also,
The potential control on the photosensitive drums 1a to 1d can be performed during this period. Then, after the fourth color visible image of the second print is transferred onto the recording material 6 conveyed by the recording material supporting belt 8 by the action of the transfer means 4d,
A post-rotation step is carried out, and in the post-rotation step, the recording material 6 is separated from the recording material carrying belt 8 and conveyed to the fixing section 7 to be collectively fixed, during which the photosensitive drums 1a to 1d are fixed.
And the recording material carrying belt 8 are cleaned.

FIG. 1A shows a pair of belt charge eliminators (charge eliminators) for removing and charging the recording material carrying belt 8.
The applied voltage in this embodiment to the inner belt static eliminator 12a (in this embodiment, a conductive brush) that is in contact with the inner side of the recording material carrying belt 8 of 12a and 12b is shown. Further, FIG. 1B shows the potential on the recording material carrying belt 8 in contact with the photosensitive drum 1d of the fourth image forming portion Pd and the transfer means 4d.

Here, in this embodiment, toner having a negative charge is used, and conductive brush-like electrodes are used for the transfer means 4a to 4d, and the conductive brush-like electrodes are recorded as shown in the figure. Contact from the inner back surface of the material carrying belt 8,
A transfer voltage was applied at a constant current of 20 μA. Further, a PET film having a thickness of 150 μm was used as the recording material carrying belt 8 and was rotationally moved at a peripheral speed of 100 mm / sec.

In the above structure, as shown in FIG. 1A, when a constant voltage of -4 KV is applied to the inner belt static eliminator 12a which is in contact with the inside of the recording material carrying belt 8, the recording material carrying belt 8 is carried. The belt 8 is charged to have a polarity opposite to that at the time of transfer (hereinafter, abbreviated as reverse charging). The recording material 6 fed from the resist roller 13 by this reverse charging is completely adsorbed on the recording material carrying belt 8 without using an adsorption charging device.

Conventionally, in an apparatus having such a structure, if the adsorption charging device is not provided, when the leading end of the recording material is curled upward, the recording material 6 is placed under the photosensitive drum 1a of the first color. When the paper is conveyed, problems such as paper breaks easily occur. Further, if the adsorption charging device is separately provided, not only an expensive circuit such as a transformer for high voltage output is increased but also a space from the registration roller 13 to the recording material carrying belt 8 being held cannot be secured. The loop of the recording material 6 formed in order to absorb the difference in the moving speed of the registration roller 13 and the recording material carrying belt 8 and to carry out stable conveyance becomes small, and the registration roller 13 and the recording material carrying belt 8 are Image unevenness occurs due to a rapid speed difference of the recording material 6 during the transfer of the recording material.

In order to avoid this, it has been proposed to control each moving speed with high accuracy, or to enlarge the device in order to maintain a space, but neither is preferable.

However, according to the present embodiment, since a predetermined constant voltage is applied to the inner belt charge eliminator 12a, the belt charge eliminator 12a removes the charge on the recording material carrying belt 8 and adsorbs the recording material 6. Therefore, the recording material 6 fed from the registration roller 13 is completely adsorbed by the recording material carrying belt 8 without the need to provide an adsorption charger, and the above-mentioned drawback does not occur.

Here, the operation of the image forming apparatus having the configuration of this embodiment will be further described with reference to FIG.

As described above, FIG. 1B shows the potential on the recording material carrying belt 8 at the transfer position of the fourth image forming portion Pd. In the sequence of the present embodiment, since the charging voltage for transfer is not applied at the time of preliminary charging,
First, the recording material carrying belt 8 which is reversely charged to -4 KV by the inner belt static eliminator 12a is the fourth image forming portion P.
When the recording material carrying belt 8 is moved to the transfer position of d, the recording material carrying belt 8 is charged to about -4 KV. However, when the recording material 6 is fed to the registration roller 13, each of the transfer means 4a to 4d applies a high voltage for transfer to the recording material carrying belt 8 at a predetermined timing. At this time, the applied voltage determines the potential on the recording material carrying belt 8. For example,
The first color was ± 0 KV, the second color was +2 KV, the third color was +4 KV, and the fourth color was +6 KV.

By the way, when the same portion on the recording material carrying belt 8 is charged by the two transfer means, as shown in FIG.
As shown in (b), it is charged from -4KV to + 2KV, when it is charged at another place it is + 4KV, and when it is charged at another place (4th color) it is + 6K.
It is charged to V. Usually, when the volume resistance value of the recording material carrying belt 8 is high resistance of 10 ¹⁵ Ω · cm or more like PET, the recording material carrying belt 8 is carried during the transfer of the visible images of the first to fourth colors. Since the electric charge on the belt 8 is hardly attenuated, a considerably high voltage must be applied during transfer. For this reason, there are drawbacks such as increased cost,
The recording material carrying belt 8 has a low resistance value or a thickness of 10
For example, a thin belt having a thickness of 0 μm or less was used.

However, in the case of the latter, there is a problem of durability due to insufficient mechanical strength and it is easy to be damaged at the time of replacement.
There is a problem in maintainability. In the former case,
There is a drawback that the transfer conditions are likely to change with respect to changes in the resistance value and the electric capacity of the recording material 6. For example, it is known that if the fiber density unevenness of the paper is in-plane, the unevenness becomes the unevenness of the recorded image.

Therefore, as in this embodiment, the recording material carrying belt 8 is reversely charged before the transfer so that the transfer voltage of the fourth color is not increased with respect to the earth of the main body, so that the good transfer can be performed. You can Furthermore, as in the configuration described in the conventional example, the belt charge eliminators 12a and 12b are not only used to remove the charge on the recording material carrying belt 8, but the charge is removed and charged on the recording material carrying belt 8 at one location. When the transfer voltage for the first color is 0V as in the example,
The transfer means 4a for the first color may be a main body or a grounded conductive electrode, so that one static eliminator performs static elimination, adsorption charging, and
It can also be used for transfer charging of colors. Therefore, the structure of the device can be simplified and the cost can be reduced. In this case, constant voltage control is applied by applying ± 0 V only for the first color,
It is preferable to perform constant current control for the second and subsequent colors. It has been conventionally known that constant current control is good in order to obtain a good transferred image even if the resistance value of the recording material 6 changes.
Particularly in the case of the first color, the recording material 6 and the recording material carrying belt 8
Since it is not used in a state in which the electric capacity of is saturated, and the electric field range with good transfer efficiency is wider than that of the fourth color, the first color is determined by grounding, which is easier to control. Voltage control is preferred.

As described above, when the transfer process by reverse charging, which has various advantages, is actually used, various problems occur in order to obtain a reliable device. One of them is a charge memory on the photosensitive drum. This is the recording material carrying belt 8
This is a phenomenon in which, when the photosensitive drums 1a to 1d are kept in contact with each other in a charged state, electric charges are accumulated on the photosensitive drums of the photosensitive drums at the contact portions, resulting in an image defect.

Therefore, in this embodiment, as shown in FIG. 1 (a), the surface potential of the recording material carrying belt 8 is set to 0 V during the post-rotation process with a voltage smaller than that during reverse charging.
A voltage of 2 KV was applied to the static eliminator 12a. For example, in FIG.
As shown in FIG. 6A, when the output of the static eliminator 12a is not controlled, as shown in FIG. 6B, the electric potential on the recording material carrying belt 8 is negatively charged, and then the electric charge is gradually attenuated. However, the higher the resistance value, the longer this decay time, and the more significant the electric charge remains.

In order to solve such a problem, in the present embodiment, a sequence is provided in which a voltage of about -2 KV is applied to the static eliminator 12a in the post-rotation step to control the surface potential to 0V. Further, in the case where the surface potential of the recording material carrying belt 8 is converged to 0 V in the structure of this embodiment, the recording material carrying belt 8 is grounded after the high voltage application to the transfer means 4a to 4d is stopped. Then, it converges to 0V much faster. As described above, the effect of the present invention becomes more effective not only by controlling the static eliminator but also by controlling the charge amount of the transfer means and the like.

In this embodiment, the recording material carrying belt 8 having a volume resistance value of 10 ¹⁵ Ω · cm or more like PET.
However, a sheet having a volume resistance value of about 10 ¹³ to 10 ¹⁴ Ω · cm, such as polyvinylidene fluoride (PVdF), has a fast charge decay rate. Therefore, in the case of the configuration shown in FIG. The distance from 12a and 12b to the feeding of the recording material 6 and the transfer position of the visible image of the first color becomes long, and the adsorbability of the recording material 6 and the above-described reverse charging effect may be diminished.

Therefore, as shown in FIG. 2, a belt charge eliminator 12a made of a conductive brush disposed inside the recording material carrying belt 8 is arranged outside the recording material carrying belt 8 near the paper feeding position. A pair of driven rollers 11a and 11b that stretches and supports the recording material carrying belt 8 is used as the belt static eliminator 12b facing this, and the driven roller 11a on the paper feed position side is used. In other words, in order to eliminate the need to additionally provide the facing static eliminator 12b, the belt static eliminator 12a is arranged outside and the driven roller 11a is used as the belt static eliminator 12b. Of course, if there is an installation place, the pair of belt static eliminators 12a and 12b may be arranged as they are near the sheet feeding position.

With this structure, the belt static eliminator 12
Since the distance from a and 12b to the feeding of the recording material 6 and the transfer position of the visible image of the first color becomes very short, the recording material 6
There is no problem that the adsorbability and the reverse charging effect are weakened. Therefore, the effect of the present invention can be more completely maintained. At this time, needless to say, a high voltage having a polarity opposite to the above-mentioned voltage is applied to the belt static eliminator 12a of the conductive brush arranged outside the recording material carrying belt 8.

Further, in the color copying machine having the structure shown in FIG. 5, the corona charger is used as the outer belt static eliminator 12b, but when the voltage applied to the outer belt static eliminator 12b is DC, Conductive brush belt static eliminator 1
It is preferable that the polarity is opposite to that of 2a. However, since it is more effective to apply an AC voltage to equalize the applied voltage, in the case of the embodiment of FIG. 1 described above, the outer belt static eliminator 12b has a peak-peak voltage of 12 KVpp and a frequency of 500 Hz. Was applied.

The present invention is more effective when applied to a color image forming apparatus in which a plurality of image forming portions as shown in FIGS. 2 and 5 are juxtaposed in a line and an image carrier dedicated to these image forming portions is used. However, the present invention is not limited to such a configuration.

Next, a second embodiment of the present invention will be described.

In this embodiment, visible images (toner images) of different colors are sequentially formed by using one photosensitive drum as an image carrier, and these toner images are formed on a drum-shaped frame body by a dielectric sheet, for example. Applied to an electrophotographic color image forming apparatus in which a color image is obtained by sequentially superposing and transferring onto a recording material held by a transfer drum as a recording material holding means stretched in a cylindrical shape, and fixing them collectively. Because if you do
First, the overall structure of such an electrophotographic color image forming apparatus will be described with reference to FIG.

The color image forming apparatus shown in FIG. 3 uses a developing device 40, which is a so-called rotary developing device, to form an electrostatic latent image formed on a photosensitive drum 41 rotating in the direction of the arrow in the figure. Develop to form a toner image. Also,
The rotary developing device 4 is provided on the outer peripheral portion of the photosensitive drum 41.
In addition to 0, in this embodiment, an exposure lamp 50, a drum charger 42 for uniformly charging the photosensitive drum 41, a polygon mirror 51 for scanning light emitted from a light source device (not shown), and a photosensitive drum. A potential sensor 52 that detects the surface potential of the body drum 41, a transfer drum 44 that carries and conveys the recording material 6, and a transfer unit 45 that transfers the visible image (toner image) on the photosensitive drum 41 onto the recording material 6. A cleaner 46 and the like for removing adhered contaminants such as toner remaining on the photosensitive drum 41 are provided.

In the electrostatic latent image forming portion, for example, a laser beam emitted from a light source device which is modulated by a color-separated image signal of cyan, for example, is scanned by rotating a polygon mirror 51, and light is reflected by a reflection mirror. A latent image corresponding to a cyan image signal is formed on the uniformly charged photoconductor drum 41 via an fθ lens that condenses the scanning light whose beam is deflected onto the generatrix of the photoconductor drum 41.

The rotary developing device 40 includes, for example, four developing devices 40a, 40b, each of which stores a four-color developer of a cyan color developer, a magenta color developer, a yellow color developer, and a black color developer, respectively. A motor (not shown) composed of 40c and 40d and a substantially cylindrical housing that holds these four developing devices 40a, 40b, 40c and 40d and is rotatably supported around a central axis. A desired developing device is conveyed to a developing position facing the outer peripheral surface of the photoconductor drum 41 by the rotation of the housing by the above, and the latent image on the photoconductor drum is developed.
It is configured such that full-color development for so-called four colors can be performed by one rotation of.

On the other hand, the recording material 6 fed from the recording material cassette 60 is temporarily stopped while being sandwiched by the pair of registration rollers 13 and is fed to the transfer drum 44 in synchronization with a predetermined timing. It At this time, the suction roller 53 arranged outside the transfer drum 44 is pressed against the transfer drum 44 by a drive source (not shown), and at the same time, the suction roller 5 is pressed inside the transfer drum 44.
A predetermined attraction voltage is applied to the attraction charger 54 arranged opposite to the recording medium 3, and the recording material 6 is electrostatically attracted to the transfer drum 44 and wound.

In this embodiment, the transfer drum 44 is a recording material made of a dielectric resin film such as a polyethylene terephthalate resin film sheet (PET sheet), a polyvinylidene fluoride resin film sheet or a polyurethane resin film sheet. Both ends of the carrying sheet 44a are joined together in conformity with the frame body to form a drum shape.

The transfer drum 44 rotates in the direction of the arrow in the figure in synchronization with the photosensitive drum 41, and the cyan developing device 4
The cyan toner image developed at 0a is transferred onto the recording material 6 by the operation of the transfer means 45 in the transfer portion. The transfer drum 44 continues to rotate in preparation for the transfer of the toner image of the next color (magenta in FIG. 3).

After the photosensitive drum 41 is cleaned by the cleaner 46, it is uniformly charged again by the drum charger 42, and is exposed by the next magenta image signal in the same manner as described above. During this time, the developing device 40 is rotated so that the magenta developing device 40b is fixed at a predetermined developing position, and predetermined magenta development is performed.

Subsequently, the same steps as described above are performed for yellow and black, and when the transfer of four colors is completed, the multi-toner image of four colors on the recording material 6 is separated and charged by the separation charger 4.
7. After the charge is removed by the peeling charger 48, the recording material 6 is
It is separated from the transfer drum 44 by operating the separation claw, and is sent to the fixing unit 7 by the conveyance belt, and the multiple composite images are fixed in a batch and discharged to the external tray. Thus, a series of full-color printing operations are completed, and the required full-color print image is output.

The fixing section 7 includes a fixing roller 71 and a pressure roller 72, heat-resistant cleaning members 73 and 74 for cleaning the rollers 71 and 72, and heaters 75 and 7 for heating the rollers 71 and 72, respectively.
6, an oil application roller 77 for applying a release agent oil such as dimethyl silicone to the fixing roller 71, an oil reservoir 78 for supplying the oil, and a thermistor 79 for controlling the fixing temperature.

After the recording material 6 is separated, the transfer drum 44 is neutralized by a pair of inner and outer sheet neutralizers (chargers for static elimination) 56a and 56b for neutralizing and charging the recording material carrying sheet 44a. Then, the recording material carrying sheet 44a is transferred by the transfer drum cleaner 55.
The adhered contaminants such as the developer remaining on the surface are cleaned. The transfer drum cleaner 55 is composed of a roller-shaped fur brush cleaner 55a arranged outside the recording material carrying sheet 44a for scraping off adhered contaminants, and a backup brush 55b arranged inside. As the cleaning member for the transfer drum cleaner 55, a blade or a non-woven fabric, or a combination thereof may be used in addition to the fur brush.

In the color image forming apparatus having the above-described structure, each rotation of the transfer drum 44 causes preliminary charging, first color toner image transfer, second color toner image transfer, third color toner image transfer, and fourth color toner image transfer. Since the post-rotation step is performed, the transfer drum 44 makes a total of 6 rotations to output one color print image. However, when the print images are continuously output, the rotation is performed 6 times only when the last print image is formed.

In this embodiment, as shown in FIG. 4A, the recording material carrying sheet of the pair of sheet charge removers 56a and 56b for discharging and charging the recording material carrying sheet 44a of the transfer drum 44. An inner sheet static eliminator 56a that is in contact with the inner side of 44a (a conductive brush in this embodiment)
On the other hand, a voltage of -4 KV was applied by pre-charging, and a voltage of about -2 KV was applied in the post-rotation process to remove the charge and reversely charge the recording material carrying sheet 44a. As a result, as shown in FIG. 4B, the same good effect as that of the first embodiment was obtained.

4 (a) shows the applied voltage in this embodiment to the inner sheet static eliminator 56a which is in contact with the inside of the recording material carrying sheet 44a of the transfer drum 44, and FIG. 4 (b). Is the photosensitive drum 41 and the transfer means 4
5 shows the electric potential on the recording material carrying sheet 44a which is in contact with No.

As described above, also in this embodiment, as shown in FIG.
As shown in (a), the surface potential of the recording material carrying sheet 44a is 0 V during the post-rotation process with a voltage smaller than that during reverse charging.
Voltage of about −2 KV was applied to the inner sheet static eliminator 56a. For example, as shown in FIG.
When the voltage (-4 KV) at the time of reverse charging is applied to the sheet charge eliminator 56a even in the post-rotation step, the potential on the recording material carrying sheet 44a is negatively charged, as shown in FIG. 7B. After that, the charge gradually attenuates, but as the resistance value increases, the decay time becomes longer, and the residual charge becomes remarkable.

In order to solve such a problem, in the present embodiment, a sequence is provided in which a voltage of about -2 KV is applied to the static eliminator 12a in the post-rotation step to control the surface potential to 0V. Further, even if the sequence in the post-rotation process is not provided or the reverse charging is not performed, the charge remains due to the positive charging.

Even in the case where the surface potential of the recording material carrying sheet 44a is converged to 0 V in the structure of the present embodiment, the high voltage application to the transfer means 45 is stopped as in the first embodiment. After that, when the recording material carrying sheet 44a is grounded, it converges to 0V even faster.

Further, in the second embodiment, a pair of inner and outer sheet static eliminators (charge eliminators) 56a and 56 are used to neutralize and charge the recording material carrying sheet 44a.
Although b is provided, the attraction roller 53 and the attraction charger 54 may be used together without providing the sheet static eliminators 56a and 56b.

The control sequence for discharging and reverse charging the recording material carrying belt 8 or the recording material carrying sheet 44a is not limited to being executed only in the post-rotation step. For example, in the color image forming apparatus shown in FIG. 4 or FIG. 5, when the recording material carrying belt 8 stops due to a defect such as a poor conveyance of the recording material 6, the recording material carrying belt 8
It may stop when the electric potential is charged. For example,
When the recording material carrying belt 8 is stopped due to a conveyance failure during transfer of the toner image of the third color, +4 KV or +6 KV is charged depending on the place. Even if you remove the recording material that caused the conveyance failure in this state,
Since the electric potential of the recording material carrying belt 8 remains, if the recording material carrying belt 8 is left in such a state, as described above, when the recording material carrying belt 8 is replaced for reasons such as the recording material carrying belt 8 being damaged or the like being damaged. In addition to causing static electricity, the recording material carrying belt 8 may stick to the main body of the apparatus and may be damaged. This is a very difficult task when it is desired to reuse, such as internal cleaning, except when it is not used again.

Therefore, in such a case, when the recording material carrying belt 8 is reset to a predetermined position, the discharging / reverse charging sequence is automatically executed, or a dedicated selection button is used. By providing the charge removal / reverse charging sequence by providing the above, the above-mentioned problem can be solved. At this time, the recording material carrying belt 8
Since the upper potential is different from the normal recording sequence,
Static electricity is removed in the same sequence as the post-rotation stroke described above with DC.
When reverse charging is performed, an excessive reverse charging state results. Therefore,
As described in the first embodiment, it was effective to use alternating current, but the effect was also obtained by controlling ± 0V constant voltage with reverse charging polarity.

In the above embodiments, the case where the present invention is applied to the electrophotographic color image forming apparatus has been described, but the present invention is not limited to this, and electrophotographic methods having various other configurations. The present invention is equally applicable to color or monochromatic (black and white) image forming apparatuses and electrostatic recording type image forming apparatuses. Further, it goes without saying that the control system, the control mode, etc. are not limited to those of the embodiment.

[0063]

As described above, according to the image forming apparatus of the present invention, the recording material carrying means is reversely charged before the visible image is transferred onto the recording material carried by the recording material carrying means. The charge removal / charging means is provided, and the potential increase of the recording material carrying means is eliminated except during the image forming operation for outputting the print image, so that the voltage rise at the time of multiple transfer is suppressed. It is possible to reduce the high-voltage output, reduce the cost, and prevent an obstacle such as discharge from occurring. Further, since the voltage rise at the time of transfer is small, there is an effect that even a dielectric material having a high resistance of 10 ¹⁵ Ω · cm or more can be used as a recording material carrying means in the form of a thick film or sheet of 100 μm or more. .

Further, since the recording material holding means is reversely charged and the reverse charging sequence is controlled so as to eliminate the residual charge due to the reverse charging, the recording material adsorbing means such as the adsorbing charging device becomes unnecessary, and further, One charge removing / charging unit can also be used for charge removal of the recording material holding unit, adsorption charging, and transfer charging of the first color, which has effects such as simplification of the apparatus configuration and cost reduction.

In addition, since the residual charge on the recording material supporting means can be eliminated, the image carrier is not charged by the residual charge, so that an image defect such as line-shaped density unevenness occurs. It can eliminate defects. Also, when replacing or maintaining the recording material carrying means, there is no defect such as electrostatically sticking to the main body of the apparatus or causing discomfort due to static electricity when touched with a hand etc. There is also an effect that the maintainability of is improved.

[Brief description of drawings]

FIG. 1 is a timing chart for explaining a sequence of control operations for charge removal / reverse charging in a first embodiment of an image forming apparatus according to the present invention.

FIG. 2 is a schematic sectional view showing an overall configuration of a first embodiment in which the present invention is applied to an electrophotographic color image forming apparatus.

FIG. 3 is a schematic sectional view showing an overall configuration of a second embodiment in which the present invention is applied to an electrophotographic color image forming apparatus.

FIG. 4 is a timing chart for explaining a sequence of control operations of static elimination / reverse charging in the second exemplary embodiment of the present invention.

FIG. 5 is a schematic sectional view showing the overall configuration of an electrophotographic color image forming apparatus to which the present invention can be applied.

FIG. 6 is a timing chart for explaining an example of a sequence of a control operation of static elimination / reverse charging in a conventional electrophotographic color image forming apparatus.

FIG. 7 is a timing chart for explaining another example of the sequence of the control operation of static elimination / reverse charging in the conventional electrophotographic color image forming apparatus.

[Explanation of symbols]

 Pa to Pd Image forming unit 1a to 1d Photoreceptor drum 2a to 2d Drum charger 3a to 3d Developing device 4a to 4d Transfer means 5a to 5d Cleaning unit 6 Recording material 7 Fixing unit 8 Recording material carrying belt 9 Transfer cleaning device 12a Inside Belt static eliminator 12b Outside belt static eliminator 16 Fur brush 17 Polygon mirror 40 Rotary developing device 41 Photosensitive drum 42 Drum charger 44 Transfer drum 44a Recording material carrying sheet 45 Transfer means 46 Cleaner 51 Polygon mirror 53 Adsorption roller 54 Adsorption charger 55 Transfer drum cleaner 56a Inner sheet static eliminator 56b Outside sheet static eliminator 60 Recording material cassette

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Yoichi Kimura 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (4)

[Claims] 1. An image bearing member on which a latent image is formed, and a developing means for developing the latent image on the image bearing member to form a visible image.
Recording material carrying means for carrying the recording material to which the visible image is transferred and conveying it to the transfer position of the image carrier, and to the recording material via the recording material carrying means at the transfer position, or the recording material An image in which a material carrying means is provided with a transfer means for applying the electric energy for transferring the visible image, and a decharging means for uniformizing the potential on the recording material carrying means is provided before the visible image transfer operation. In the forming apparatus, the decharging means is controlled so that the electric potential on the recording material carrying means becomes the reverse electric potential at the time of the transfer operation during the image forming operation for outputting a print image, and during the time other than the image forming operation. The image forming apparatus is characterized in that the electric potential on the recording material carrying means is controlled to be 0 with respect to the apparatus main body. 2. The image forming apparatus is a color image forming apparatus which outputs a multicolor image by sequentially superposing and transferring a plurality of visible images of different colors on a recording material held by the recording material carrying means. When the visible image of the first color is transferred onto the recording material, the transfer means is subjected to constant voltage control, and when the visible images of the second color and after are transferred, the transfer means is subjected to constant current control. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. 3. The recording material holding means of the recording material holding means is composed of a dielectric sheet, and the volume resistance value of the dielectric sheet is 10 ¹⁵ Ω · cm or more. The image forming apparatus according to Item 1 or 2. 4. A static elimination sequence of the recording material carrying means is set separately from the image output, and the separate static elimination sequence can be executed at a predetermined timing or by a dedicated operating means. The image forming apparatus according to claim 1.