JP2001051473A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prolong a service life of image forming means by re-using recovered toner, and to dispense with a cleaner by recovering the residual toner on a photosensitive drum without causing color contamination by the simultaneous developing and cleaning method. SOLUTION: Relating to first to fourth image forming units Pa to Pd arranged along a transfer belt 10, a cleaner of the photosensitive drum 1 is not arranged, the cleaner is dispensed with in a simultaneous developing and cleaning method without providing the cleaner for the photosensitive drum 1, the residual toner on the drum 1 is uniformized by the uniformized member 16, and the toner is recovered at the time of developing by the developing device 6, so that the drum 1 is cleaned. At this time, in order to prevent the toner image on the transfer paper T from being respectively transferred again, on drums 1 of units Pa to Pd on the downstream side except the first unit Pa, a corona discharger 13 is arranged between respective unit Pa to Pd mutually adjoining, so that the toner image subjected to reverse polarity on the transfer paper T is turned to have the primary normal charge polarity to make the polarity of toner uniform.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an in-line type color image forming apparatus using an electrophotographic method.

[0002]

2. Description of the Related Art Conventionally, an in-line type color image forming apparatus to which electrophotography is applied, as shown in FIG.
Four image forming units (image forming units) Pa, Pb, Pc, and Pd each having the photosensitive drum 1 are provided along a transfer belt 10 that is a transfer material conveying unit. Each of the units Pa to Pd includes a charger 4, an exposure device 5, a developing device 6, a transfer device 11 and a drum cleaner 12 around the photosensitive drum 1.
Having.

In order to form an image, the surface of the photosensitive drum 1 is charged by a charger 4, an image pattern is irradiated with light by an exposure device 5 to form an electric latent image, and the latent image is developed by a developing device 6. The toner is developed and visualized as a toner image to which toner (charged particle colored developer) is attached. The toner images of the respective colors obtained on the respective photosensitive drums 1 are superimposed and multiply transferred by a transfer device 11 on a transfer material (usually paper) T which is carried and conveyed on a conveyor belt 10. .

Normally, for example, the first unit Pa has a yellow toner image, the second unit Pb has a cyan toner image,
A magenta toner image is formed by the unit Pc, and a black toner image is formed by the fourth unit Pd.
A color image is obtained by superimposing and transferring four color toner images of magenta, cyan, and black.

The transfer material T onto which the toner image has been transferred is separated from the transfer belt at the downstream end of the transfer belt 10 in the transfer material transfer direction, is transferred to a fixing device (not shown), and is fixed there by heating and pressing. This is a full-color print image.

The photosensitive drum 1 after the transfer is cleaned by a cleaner 12 to remove the transfer residual toner on the surface, and is used again for image formation. The removed transfer residual toner is stored in the container of the cleaner 12 as waste toner.

[0007]

As described above, in the above-described conventional image forming apparatus, the drum cleaner 12 is provided on the photosensitive drum 1 to clean the transfer residual toner on the photosensitive drum 1, so that the transfer is not performed. 1 for cleaning residual toner
There has been a problem that the price of an image per sheet increases.

Therefore, conventionally, a leveling member or the like is provided for the photosensitive drum without providing a dedicated drum cleaner, so that the transfer residual toner on the photosensitive drum is leveled evenly on the surface, and collected in a developing device at the time of development. A cleaner-less system using simultaneous development and cleaning has been devised.

However, in the image forming apparatus that performs the multiple transfer as described above, the toner transferred onto the transfer material is reversed on the surface of the photosensitive drum at the transfer section of the image forming unit on the downstream side in the transfer material traveling direction. Copying and color mixing of toner occur in the developing device of the downstream image forming unit with long-term use. For this reason, a change in tint occurs during development, and the quality of a color image is impaired.

Accordingly, an object of the present invention is to recover the residual toner on the photosensitive drum without causing color mixture by the simultaneous development cleaning method, and to extend the life of the image forming means by reusing the recovered toner. Another object of the present invention is to provide an image forming apparatus capable of making a photosensitive drum cleanerless.

[0011]

The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides:
A plurality of image forming units including an image carrier, a charger, an exposure unit and a developing unit are arranged along the rotating transfer material conveying unit,
In an image forming apparatus, a plurality of color toner images obtained on a plurality of image carriers of the plurality of image forming units are transferred by being superimposed on a transfer material conveyed by the conveying unit.
At least one image forming unit among the plurality of image forming units does not include a cleaning unit for the image carrier, and the image forming unit that does not include the cleaning unit is provided upstream of the transfer material in the conveyance direction of the transfer material. An image forming apparatus is provided with a charge applying means for making the charging polarity of the toner image uniform.

According to the present invention, the image forming means without the cleaning means is capable of dispersing the residual toner on the image carrier by the leveling member and simultaneously recovering the dispersed toner by the developing unit. The carrier is cleaned.
Further, when the image forming unit without the cleaning unit is the image forming unit that is located at the most upstream position in the transport direction of the transfer material, the charge applying unit is not provided. An image forming unit having a high image forming frequency is an image forming unit that does not include the cleaning unit. The transfer material transporting means comprises an endless belt. Furthermore, an intermediate transfer member that rotates in place of the transfer material conveying unit is provided, and a plurality of color toner images obtained on a plurality of image carriers of the plurality of image forming units are superimposed on the intermediate transfer member. And then collectively transfer onto the transfer material conveyed to the intermediate transfer member.

[0013]

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

Embodiment 1 FIG. 1 is a schematic structural view showing an embodiment of the image forming apparatus of the present invention.

As shown in FIG. 1, the image forming apparatus includes four image forming units (image forming units) each having a photosensitive drum 1 along a transfer material conveying belt (transfer belt) 10.
Pa, Pb, Pc, and Pd are provided. Each of the image forming units Pa to Pd has basically the same configuration.

In this embodiment, a drum-shaped electrophotographic photosensitive member as an image carrier, that is, a photosensitive drum 1 is provided on a metal cylinder 2 as an organic semiconductor (OPC), AS
An optical semiconductor layer 3 of i, Se, or the like is applied or deposited. In this embodiment, an OPC photosensitive member was used. The photosensitive drum 1 has a diameter of 30 mm, and is rotationally driven by a driving source (not shown) at a peripheral speed of 130 mm per second in the direction of the arrow.
The surface is uniformly charged to a predetermined potential by the charging roller 4.

The charging roller 4 is disclosed in JP-A-57-12826.
7, 56-104351, 58-40566, 58-1
As disclosed in JP 39156, 58-150975, a DC voltage of -700 V is applied from a power supply (not shown). If necessary, a sine wave, a rectangular wave, a triangular wave, or the like having a frequency of 1600 Hz and a peak-to-peak voltage of 1200 V may be superimposed. Thereby, the surface of the photosensitive drum 1 becomes
It is charged to approximately -700V.

Next, an electrical latent image for each color is formed on the surface of the photosensitive drum 1 by the optical imaging unit 5. As the optical imaging unit 5, a combination of an LED element and an optical lens, a combination of a laser diode, an optical lens, a rotating mirror and a mirror, or a combination of PLZT and a liquid crystal can be used. In the present embodiment, an electric latent image was formed on the photosensitive drum 1 by using an optical imaging unit combining a laser diode and the like, and inputting an electric signal from an image signal generator (not shown) to the laser diode. .

Incidentally, the electric latent image was formed in a reversal type in which the toner adheres to a portion of the photosensitive drum 1 to which light is applied. At this time, the portion irradiated with light was formed at a potential of approximately -100 V, and the intermediate reproduction region was formed at a potential in the range of -700 V to -100 V.

The electrostatic latent image on the photosensitive drum 1 reaches the developing unit 6 by the rotation of the photosensitive drum 1 and is developed by the developing unit 6 to be visualized as a toner image. Thus,
First to fourth color toner images are formed on the photosensitive drums 1 of the image forming units Pa to Pd. As a developing method of the developing device 6, one-component jumping development, one-component contact development, two-component development, cascade development, spray development, or the like can be used. In the present invention, one-component jumping development is employed.

The developing device 6 is provided with a metal cylindrical sleeve (developing sleeve) 8 having a diameter of 16 mm facing the photosensitive drum 1 in a developing container 7. The developing sleeve 8 is rotated in the direction of the arrow at a peripheral speed of 160 mm per second. As a result, the toner (one-component developer) contained in the developing container 7 is carried and conveyed on the developing sleeve 8, regulated by the doctor blade 9, and uniformly applied to the developing sleeve 8. 250 μm between the developing sleeve 8 and the photosensitive drum 1
, The developing sleeve 8 and the photosensitive drum 1
When an alternating electric field obtained by superimposing an AC voltage having a frequency of 1400 kHz and a peak-to-peak voltage of 1200 V on a DC voltage of -400 V as a developing bias is applied, the toner on the developing sleeve 8 flies to the photosensitive drum 1 and the toner is And develop. As the toner, an image is formed using, for example, a four-color toner having a brand name of LBP2160 commercially available from Canon Sales Co., Ltd.

The toner images of the respective colors formed on the respective photosensitive drums 1 are superimposed on the transfer paper T carried and conveyed on the transfer belt 10 by the transfer rollers 11 at the respective transfer portions. Is transferred to form a color image in which four color toner images are superimposed on the transfer paper T. The transfer roller 11 has substantially the same configuration as the charging roller 4, and is disposed on the back surface of the transfer belt 10 so as to face the photosensitive drum 1. At the time of transfer, the photosensitive drum 1 and the transfer roller 11
During this time, a DC voltage is applied such that the voltage on the transfer roller 11 side is -800V.

The transfer belt 10 is made of PVd having a thickness of 100 μm.
It is made of an F film and moves in synchronization with the photosensitive drum 1. The thickness and material of the transfer belt 10 are not limited to the above, and the thickness can be selected from a range of 50 to 200 μm. The material may be a material other than PVdF, such as carbon or the like dispersed in a rubber material such as EPDM. Or the electric capacity may be adjusted.

Transfer material T on which four color toner images are superimposed and transferred
Is separated from the transfer belt 10 and sent to a fixing device (not shown), where the toner image is fixed by heating and pressurizing, and is discharged out of the image forming apparatus as a full-color print image.

Each photosensitive drum 1 after the transfer of the toner image is prepared for the next image formation by removing the residual toner on the surface. In this embodiment, the first to fourth image forming units P
No special cleaner for the photosensitive drum 1 is installed in a to Pd.
A residual toner is evenly leveled on the surface of the photosensitive drum 1 by the toner leveling member 16, and then the residual toner is collected in the developing device 6 at the time of development to clean the photosensitive drum 1. I am taking.

The toner leveling member 16 has a thickness of, for example, 10
It is made of a sheet of 0 μm PET (polyethylene terephthalate) or the like, and is in contact with the surface of the photosensitive drum 1 to level the residual toner on the surface of the rotating photosensitive drum 1 so as not to block the optical path from the optical imaging unit 5. Disperse residual toner.

In an image forming apparatus that performs multiple transfer as described above, conventionally, the toner transferred on the transfer material is transferred to the surface of the photosensitive drum by the transfer unit of the image forming unit on the downstream side in the transfer material traveling direction. Had the problem of reverse transcription. This is because, for example, when the first color toner image from the photosensitive drum 1 is transferred to the transfer paper T in the first image forming unit Pa, the photosensitive drum 1 and the transfer paper T are separated from each other. Since the separation discharge occurs between the sheet T and the paper T, the charge due to the separation discharge adheres to the first color toner image, and a part of the toner polarity is reversed to be positive. When the image is transferred to the transfer paper T, the inverted first color toner is reversely transferred to the photosensitive drum 1.

For this reason, if the drum cleaner is not provided in the downstream image forming unit, the reversely transferred toner enters the developing device from the photosensitive drum, and the toner is transferred to the downstream developing device with long-term use. And the color tone of the image is changed by the development by the developing device on the downstream side, and the quality of the color image is impaired. Therefore, it has been difficult to realize the cleaner-less operation conventionally.

Therefore, in this embodiment, as shown in FIG. 1, between the first and second image forming units Pa and Pb, between the second and third image forming units Pb and Pc, and between the third and fourth image forming units Pb and Pc.
Corona chargers (charge injection corona dischargers) 13 are respectively installed between the image forming units Pc and Pd so as to face the transfer belt 10, and the toner images transferred onto the transfer paper T are transferred from the corona chargers 13. A charge having the same polarity as the charge polarity of the toner is injected, and the toner whose polarity has been inverted by the peeling discharge at the time of transfer of the toner image is returned to the original normal charge polarity, so that the toner polarity is made uniform.

The corona charger 13 is made of a metal plate made of aluminum or the like.
4 and a diameter of 60 μm
Corona wire 15 is arranged. When a DC voltage of −6000 V having the same polarity as the toner is applied to the corona wire 15,
The toner whose polarity has been inverted from the toner image on the transfer paper T can be returned to the normal polarity.

In this way, the 1 transferred on the transfer paper T
The toner polarity of the color toner image is aligned by charging by the charger 3, and the second color toner image formed on the photosensitive drum 1 by the image formation in the second image forming unit Pb is transferred to the transfer unit of the second image forming unit Pb. The toner of the first color did not adhere to the photosensitive drum 1 even when it was transferred onto the transfer paper T conveyed to the photosensitive drum 1.

Similarly, after the toner image of the second color is transferred onto the transfer paper T, the polarity of the toner is made uniform by charging by the charger 3, so that the toner of the third color on the photosensitive drum 1 of the third image forming unit Pc is formed. Even if the image is transferred over the transfer paper T,
The toner of the first color and the toner of the second color do not adhere to the photosensitive drum 1, and after the toner image of the third color is transferred onto the transfer paper T,
Even if the toner image of the fourth color on the photosensitive drum 1 of the fourth image forming unit Pd is superimposed and transferred onto the transfer paper T by aligning the polarity of the toner by charging by the charger 3, the first color is transferred to the photosensitive drum 1. No adhesion of the second and third color toners was observed.

Therefore, in this embodiment, even if the drum cleaner for the photosensitive drum 1 is not installed in the second to fourth image forming units Pb to Pd on the downstream side, not only the first image forming unit Pa, but also It is possible to prevent color mixing of the toner used in the image forming unit on the upstream side in the image forming unit 6, and to develop the image satisfactorily without changing the color in all the developing units 6 of the image forming units Pa to Pd. And a high-quality color image can be obtained.

That is, according to the present embodiment, in each of the image forming units Pa to Pd, the leveling member 16 uniformly levels the residual toner on the photosensitive drum 1 and the leveled toner in the developing device 6. It is possible to realize cleaner-less cleaning based on the simultaneous cleaning with development by collecting at the time of development. Further, in the second to fourth image forming units Pb to Pd on the downstream side as well as in the first image forming unit Pa, the collected toner in the developing device 6 has no color mixture, so the collected toner can be used again for development. The life of these developing units, and thus the life of the image forming unit, can be extended.

Embodiment 2 FIG. 2 is a schematic diagram showing another embodiment of the image forming apparatus of the present invention.

In this embodiment, the uppermost-stream first image forming unit Pa, which does not involve retransfer of the toner used in the image forming unit on the upstream side, is made cleaner-less, The photosensitive drum 1 is cleaned by a simultaneous development cleaning method in which the residual toner is leveled and the leveled toner is collected at the time of development in the developing device 6.

Second to fourth image forming units Pb to Pd
The photosensitive drum 1 is controlled by the drum cleaner 12 as in the prior art.
Was cleaned.

The cleaner-less first image forming unit Pa is preferably a unit having a high image forming frequency in which the usefulness of the reuse of the toner collected in the developing unit 6 is large, and in this embodiment, The first image forming unit Pa is a black image forming unit, and the capacity of the developing unit 6 is larger than the developing units 6 of the other image forming units Pb to Pc. The second to fourth image forming units Pb to Pd can be image forming units having a lower image forming frequency toward the downstream side. For example, the second image forming unit is Pb, magenta, and the third image forming unit Pc. Is a cyan image forming unit and the fourth image forming unit Pd is a yellow image forming unit.

According to the present embodiment, the frequently used image forming unit is used as the first image forming unit Pa, the cleaner is eliminated by the simultaneous development cleaning method, and the collected toner is reused. The advantage of extending the life of the image forming unit is great, and the cost can be greatly reduced. Further, according to the leveling member 16, since the surface of the photosensitive drum 1 is not rubbed with a strong force unlike the cleaner 12, even if the photosensitive drum 1 is frequently used,
It is also possible to prevent the surface of the photosensitive drum 1 from being displaced or damaged.

In the above, the first image forming unit Pa is used as an image forming unit which is frequently used, and the photosensitive drum 1
Is cleaned by the simultaneous development method, but if any one of the image forming units Pb to Pd on the downstream side is frequently used, the drum cleaner 12 is not provided in the frequently used image forming unit. A cleaner-less cleaning system is used to remove the cleaner. At this time, a corona charger 13 similar to that of the first embodiment is installed between the frequently used image forming unit and the image forming unit on the upstream side thereof. What is necessary is just to make the toner charging polarity of the toner image transferred onto the transfer paper T by the charger 13 uniform.

As described above, the first image forming unit Pa does not have the function of shaving the photosensitive drum surface by the cleaning blade, and each of the image forming units Pa to Pd
Even if the photosensitive drum 1 is the same, the life of the photosensitive drum without the cleaner 12 is prolonged. Therefore, by increasing the developing device of the image forming unit without the cleaner 12 and increasing the toner, the life of the image forming unit is reduced. Can be easily extended.

In each of the first and second embodiments, the image forming apparatus uses the transfer paper T on the transfer belt 10 to transfer a plurality of color toner images obtained by the plurality of image forming units Pa to Pd.
Although the transfer is performed by directly superimposing the image on the intermediate transfer drum, the present invention installs a rotating intermediate transfer drum instead of the transfer belt, and superimposes a plurality of color toner images obtained by a plurality of image forming units on the intermediate transfer drum. The present invention can also be applied to an image forming apparatus of a system in which transfer is performed together, and then collective transfer from the intermediate transfer drum onto a transfer material conveyed to the intermediate transfer drum. Instead of the transfer belt or the intermediate transfer belt, a drum in which a dielectric layer or the like is provided on a metal drum base by coating or pasting may be used.

Although the toner is not mentioned, a polymerized toner as disclosed in Japanese Patent Application Laid-Open No. 2-73366 can be employed, and a greater effect can be obtained.

The polymerized toner contains a polyester resin produced from the following monomer composition. The polyester resin has a hydroxyl value of 10 to 20, a weight average molecular weight (Mw) of 13,000 to 20,000, It has a component having a number average molecular weight (Mn) of 5,000 to 8000 and a weight average molecular weight (Mw) / number average molecular weight (Mn) ratio of 2 to 3.5. It is created by mixing a yellow colorant. In a black toner, carbon black or the like is mixed instead of the colorant. Magnetite or the like is mixed into the black toner as needed.

The monomer composition contains a divalent aromatic acid component selected from isophthalic acid, terephthalic acid and derivatives thereof in an amount of 25 to 35 mol% of the total monomer amount, and trimet acid and derivatives thereof. 2 to 4 mol% of the total amount of the monomeric trivalent aromatic acid component, dovicenyl succinic acid,
It contains at least 45 to 60 mol% of a divalent system acid component selected from octylic acid and anhydride thereof based on the total amount of monomers.

Since the toner made of the above-mentioned materials, particularly the polymerized toner, has a high transfer efficiency, the burden of cleaning on the photosensitive drum 1 can be reduced, and this is more convenient for achieving cleaner-less as in the present invention. .

[0047]

As described above, according to the present invention,
For a plurality of image forming units provided along the transfer material conveying unit or the intermediate transfer body, at least one of the image forming units is not provided with a cleaning unit for the image bearing member, and the image bearing member is cleaned by the simultaneous development and cleaning method. At this time, a charge applying unit is provided upstream of the image forming unit without the cleaning unit, and the toner having the polarity inverted from that of the toner image transferred onto the transfer material or the toner image transferred onto the intermediate transfer body is originally used. Since the charging polarity is returned to the normal charging polarity, the toner is not retransferred from the toner image to the image carrier, and the residual toner on the image carrier generates color mixture by a simultaneous development and cleaning method. The image forming means can be collected and reused without being used, so that the life of the image forming means can be extended and cleaner can be eliminated.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing one embodiment of an image forming apparatus of the present invention.

FIG. 2 is a schematic configuration diagram showing another embodiment of the image forming apparatus of the present invention.

FIG. 3 is a schematic diagram illustrating a conventional image forming apparatus.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 photosensitive belt 4 charging roller 6 developing device 10 transfer belt 11 transfer roller 13 corona charger 16 toner leveling member T transfer paper

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H030 AA06 AB02 AD02 AD03 AD05 BB23 BB42 BB44 2H032 AA05 BA03 BA09 BA18 BA27 CA01 CA13 2H077 AD02 AD06 BA10 DB14 EA13 EA14 EA16 EA24 GA13 2H078 AA29 BB01 DD40 DD42 DD03 DDDD EE27

Claims (6)

[Claims] 1. A plurality of image forming means including an image carrier, a charger, an exposing device, and a developing device are arranged along a rotating transfer material conveying means, and a plurality of image carriers of the plurality of image forming means are provided on the image carrier. An image forming apparatus that superimposes and transfers a plurality of color toner images obtained on a transfer material conveyed by the conveyance unit, wherein at least one of the plurality of image formation units is an image carrier A charge applying means for aligning the charging polarity of the toner image on the transfer material on the upstream side of the image forming means without the cleaning means with respect to the transfer direction of the transfer material. Image forming apparatus. 2. An image forming apparatus having no cleaning means, wherein the residual toner on the image carrier is dispersed by a leveling member, and the dispersed toner is simultaneously collected and developed by a developing device to clean the image carrier. The image forming apparatus according to claim 1, wherein: 3. The image forming apparatus according to claim 1, wherein the image forming unit not provided with the cleaning unit is an image forming unit positioned at the most upstream position in a transfer direction of the transfer material. Image forming apparatus. 4. The image forming apparatus according to claim 1, wherein the image forming unit having a high image forming frequency is an image forming unit without the cleaning unit. 5. The image forming apparatus according to claim 1, wherein said transfer material conveying means comprises an endless belt. 6. An intermediate transfer member which rotates in place of said transfer material conveying means, and transfers a plurality of color toner images obtained on a plurality of image carriers of said plurality of image forming means onto said intermediate transfer member. The image forming apparatus according to claim 1, wherein the image is transferred by being superimposed on the image, and then transferred onto the transfer material conveyed to the intermediate transfer body at a time.