JPH03177866A - Color image forming device - Google Patents

Abstract

PURPOSE:To improve conveyability and separability by disposing the opening part of a paper electrifier, which is provided on a wedge-shaped space part formed by an image carrier and a belt part, so as to be confronted with the belt. CONSTITUTION:The paper electrifier 60 is provided on the wedge-shaped space part formed by the image carrier 10 and the belt part 10, and the opening part 64 of the paper electrifier 60 is disposed so as to be confronted with the belt 71. Therefore, the paper electrifier 60 carries out corona discharges to transfer paper P, which is fed by a resist roller 53, at a position confronted with a roller 72, the electrification is efficiently and surely carried out by using the roller 72, which is almost brought into contact with the earth, as an opposite electrode, and moreover, a distance to a transfer part can be shortened. Thus, the transfer paper P can be carried being firmly attracted and held by the transfer belt 71, and the separability of the transfer paper P from a photosensitive drum 10 can be always preferably maintained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a transfer material for an image forming apparatus such as an electrophotographic copying machine,
The present invention relates to a color image forming apparatus having a transfer belt device that electrostatically supports and transports a toner image on an image carrier, transfers it onto the transfer material by physical means, and then transports the toner image to a fixing means.

Prior Art] FIG. 6 is a cross-sectional configuration diagram showing an embodiment of a conventional electrophotographic copying machine. In the figure, IO is a photosensitive drum which is a drum-shaped image carrier, 20 is a charger that charges the circumferential surface of the photosensitive drum 10, 30 is an exposure device, 13 is an image exposure section, 40 is a developing device, and 50 is a transfer device. A material supply device, P is a transfer paper which is a transfer material, 16 is a transfer charger, 17 is a separation charger, 80 is a fixing device, 90 is a cleaning device, and 56 is a conveyor belt which is a means for conveying the transfer paper P. be.

To explain the operation of the copying machine, after the charger 20 uniformly charges the circumferential surface of the photoreceptor drum 10, the photoreceptor drum 1
The exposure device 30 performs exposure in the image exposure section 13 on the zero peripheral surface to form an electrostatic latent image. Thereafter, the latent image is developed and visualized by the developing device 40 to become a toner image. This toner image is transferred onto the transfer paper P fed by the transfer material supply device 50 at the same timing. This transfer is performed by charging the transfer paper P from behind with a transfer charger 16 with a polarity opposite to that of the toner. After the transfer, a high AC voltage is applied by the post-transfer separator 17 to eliminate static electricity, and the transfer paper P is separated from the photoreceptor drum IO. The separated transfer paper P is conveyed to a fixing device 80 by a conveyor belt 56, and the toner image thereof is fixed and discharged from the apparatus.

On the other hand, the photosensitive drum 10 to which the toner image has been transferred is cleaned by a cleaning device 90 to remove toner remaining on the circumferential surface.

However, in the above configuration, in order to ensure the transferability and separation of the toner image, it is necessary to find the optimal function by adjusting the discharge efficiency between the transfer charger 16 and the separator 17. , and this discharge efficiency is greatly influenced by the environment, and the tolerance range for reliability is narrow. The transferability is influenced by the electric charge of the transfer paper P and the mechanical properties of the transfer paper P (stiffness 0 surface smoothness, curl, etc.), and these are influenced by the storage condition of the transfer paper P and the environment at the time of transfer ( It fluctuates greatly depending on factors such as temperature and humidity, making it difficult to maintain it in good condition at all times.

Furthermore, when the drum diameter of the photosensitive drum IO is large, when the transfer paper P moves to the conveyor belt 1-30, the force to return to the original flat state is smaller than when the drum diameter is small, so that the toner The transfer paper P after the image transfer is likely to adhere to the photoreceptor drum IO and cause a paper jam, resulting in a decrease in the paper passing ability of the machine and deteriorating its reliability.

A belt-shaped transfer/conveying device shown in FIG. 7 is disclosed as a technique for improving the above-mentioned drawbacks in US Pat. No. 3,357,325 and the like.

In FIG. 7, 10 is a photosensitive drum which is a drum-shaped image carrier, 71 is a transfer belt made of a single dielectric layer, and 72 and 73 are belts for supporting, extending and rotating the transfer belt 1-71. A roller 79 is a roller for guiding the transfer paper P, and 60 is a roller for guiding the transfer paper P by electrostatic force.
Paper charger that performs corona discharge to adsorb to 21, 16
Reference numeral 160 indicates a transfer charger for transferring the toner image from the photosensitive drum 10 to the transfer paper P, and 160 indicates a transfer section. With this configuration, the transfer paper P can be firmly attached to the transfer belt 71 and transported reliably, and excellent transfer efficiency and separation efficiency can be obtained.

The belt-shaped transfer/transport device is particularly suitable for the photosensitive drum 1.
This is a preferred color image forming apparatus in which a toner image is formed on top of a toner image and transferred to the transfer paper P all at once. In the above-mentioned color image forming apparatus, since the toner images are superimposed on the photoreceptor drum 10, the diameter of the drum becomes thicker, and since sufficient separation performance cannot be obtained with the conventional electrostatic transfer separation method, more reliable separation performance is required. If the toner images are overlapped, the amount of toner adhesion will increase.
This is because a belt-type transfer/transport device is superior in two respects: since a large amount of transferred charge is required, it is necessary to have a large transfer charge holding ability.

[Problem to be solved by the invention]

The transfer/transport device (transfer belt device) shown in Fig. 7,
The transfer paper P and the transfer belt 1-71 are charged by the paper charger 60 and attracted to each other, and the transfer paper P is conveyed as the transfer belt 71 moves. During charging, -5, C: 0 sleeve φζ 100/f, -6 ↑Gift width η (1) There is a problem that transport becomes unstable.

To solve this problem, the paper charger 50 is installed in the transfer section 160.
However, the space near the transfer section 160 has a wedge-shaped cross section formed by the photosensitive drum 10 and the transfer belt 71. In addition, a paper charger 60
Since a high voltage of 5 to 5 KV is applied to the discharge wire, the distance between the discharge wire and the back plate, which is a shielding member, must be 6 to 7 mm or more. Therefore, there are certain restrictions on reducing the size of the conventional paper charger 60, and it must be placed at a certain distance from the transfer section 160, which is especially true for color image forming apparatuses equipped with a large number of developing devices. In this case, the drum diameter of the photoreceptor drum IO becomes larger, so the space between the transfer belt 71 and the photoreceptor drum 10 becomes a wedge-shaped cross-sectional space with an acute apex, and the paper charger 60 is installed away from the transfer section 160. However, it has been impossible to solve the problem.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to provide a color image forming apparatus with excellent conveyance performance and 9 studs, 1 reciprocal belt, 2 belts, and 4F.

[Means to solve the problem]

The purpose is to arrange a plurality of developing devices with different toner colors on the peripheral edge of a rotating image carrier, to sequentially perform reversal development using the developing devices, to superimpose toner images on the image carrier, and then transfer the toner images. In a color image forming apparatus that transfers images onto a material using a transfer belt device, a paper charger is provided in a wedge-shaped space formed by the image carrier and the belt, and an opening of the paper charger is opposed to the belt. It is distantly related to the color image forming apparatus, which is characterized by being arranged as follows.

〔Example〕

FIG. 1 is a sectional view showing the structure of an embodiment of a color image forming apparatus of the present invention.

In the figure, IO is a drum-shaped image carrier, that is, a photosensitive drum, which is coated with an OPC photosensitive member, and is grounded and rotated clockwise.

20 is a scorotron charger that applies an electric charge to the photoreceptor on the circumference of the photoreceptor drum 10; 13 is an image exposure light or a laser beam that is focused on the photoreceptor drum 10 by an exposure optical system (not shown); This is the image exposure section where the image is projected.

For example, a laser writing system unit is used as the exposure optical system. When a color signal output from an image reading device separate from the image forming device is input to the laser writing system unit, the laser beam (wavelength 78
0 nm) is rotated and scanned by a polygon mirror, the optical path is bent by a reflection mirror via an fθ lens, and the photosensitive drum 10 is uniformly charged in advance by the charger 20.
Projected onto the surrounding surface.

On the other hand, when scanning is started, the laser beam is detected by the index sensor, modulation of the laser beam by the first color signal is started, and the modulated laser beam scans the circumferential surface of the photoreceptor drum 10. Therefore, a latent image for the first color is formed in the image area on the photoreceptor drum IO by the main scanning by the laser beam and the sub-scanning by the rotation of the photoreceptor drum 10. This latent image is reversely developed by a developing means containing toner of, for example, yellow (Y) as a first color, and a yellow toner image is formed on the circumferential surface of the photoreceptor drum 10. The obtained toner image in the image area is transferred to the photoreceptor drum 1 while being held on the circumferential surface of the photoreceptor drum 10.
It passes under the transfer means and cleaning means which are separated from the circumferential surface of 0, and enters the next copy cycle.

That is, the photosensitive drum lO is charged again by the charger 20, and then the second
The color signal is input to the writing system unit, and the second color signal is written on the circumferential surface of the photoreceptor drum 10 in the same manner as in the case of the first color signal described above to form a latent image. This latent image is subjected to reversal development by a developing means containing toner of magenta (M) as a second color, for example,
A magenta toner image is formed. This magenta toner image is formed on top of the previously formed yellow toner image. Therefore, the magenta toner partially overlaps the yellow toner.

The toner image of the image area obtained in this way is held on the circumferential surface of the photoreceptor drum 10 and passes under the transfer means and the cleaning means which are separated from the circumferential surface of the photoreceptor drum 10, and is used for the next copy cycle. to go into.

Similarly, writing is performed on the photosensitive drum 10 using the third color signal to form a latent image. This latent image is subjected to reversal development by a developing means containing toner of a third color, for example, cyan (C).

A color image is obtained by forming this cyan toner image on top of the yellow and magenta toner images described above. Furthermore, a developing means containing black toner may be provided, and a high-quality color image may be obtained by further superimposing black toner images in the same manner as described above.

Developing units 41 to 43 are developing units that contain yellow, magenta and cyan toners for performing the above-mentioned development, and all have similar structures.

FIG. 2 shows the structure of the developing device 41.
Inside the developing sleeve 411. Magnet roller 4
12. Stirring screws 413, 414, scraping plate 415
etc. are provided. The gap between the developing sleeve 411 and the photoreceptor drum 1O is determined by a roller (abutting outside the image area of the circumferential surface of the photoreceptor drum 10 provided coaxially with the developing sleeve 411).
(not shown) to maintain a constant gap of around 0.5 mm.

Toner is replenished from a toner storage device (not shown).
The mixture is thoroughly stirred and mixed with the magnetic carrier by a stirring spoon 414 and a stirring screw 413 that rotate in opposite directions. After this two-component developer consisting of magnetic carrier and toner is stirred and mixed, the developing sleeve 411
is supplied to A magnet roller 412 having a fixed magnetic pole is disposed inside the developing sleeve 411, and the above-described thin layer of developer is formed by the developing sleeve 411 and the magnet roller 412.

For example, a cylinder made of a magnetic material is provided facing the magnetic pole of the magnet roller 412 so that the thickness of the thin layer of developer on the surface of the developing sleeve 411 is thinner than the gap between the developing sleeve 411 and the photosensitive drum IO. By pressing the developer thin layer forming means 416 of the rod against the developing sleeve 411, the developer layer is shaped into an even thin layer of about 300 μm. A developing bias is applied to the developing sleeve 411,
The latent image in the image area on the photosensitive drum 10 is developed. After the development has been completed, the thin layer of developer on the developing sleeve 411 is once scraped off by the scraping plate 415, and a new thin layer of developer is formed by the method described above.

Charging by the charger 20 provided on the photosensitive drum 10 and its periphery, exposure by the laser writing system unit for each color, and development by the developing devices 41 to 43 are performed three times for each color, and the photosensitive drum 10 is A color toner image is formed on the image area on the circumferential surface of the body drum IO by overlapping.

Reference numerals 51 and 52 refer to passages for transfer paper, which are transfer materials according to size, fed one by one from a transfer material supply device, and 53 a transfer section 160 in synchronization with the movement of the color toner image on the photoreceptor drum 10. These are registration rollers for conveying the transfer paper to the paper.

70 is a transfer belt device, 71 is a transfer belt which is a belt portion, 72 and 73 are rollers made of conductive metal material,
The upstream roller 72 is a roller that has a rotatable shaft that is at a predetermined potential that is grounded or close to the grounded state, and the downstream roller 73 is a roller that drives the transfer belt 71 and has a fixed shaft. Reference numeral 74 denotes a belt support member, one end of which has the axis of the roller 73 as a fixed shaft, and the other end connected to the movable shaft of the roller 72, and is connected to the roller 72 by an elastic member (not shown).
is biased so that it is positioned downward. Therefore, the transfer belt 71 is normally retracted from the circumferential surface of the photoreceptor drum 10, and during transfer, the eccentric cam 77, which is operated under the control of the device control section, is attached to the belt support member 74 via the leaf spring 78.
is pressed upward in the figure, rotates counterclockwise around the roller 73, and the rollers 76 provided at both ends of the belt support member 74 move the side edges of the circumferential surface of the photoreceptor drum 10 outside the image area. The transfer bell 1-71 is in contact with the photoreceptor drum I.
It comes into contact with the transfer section 160 of O.

7 is for scraping off the adhered toner on the transfer belt 71.
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A toner conveying pipe having a flexible conveying screw inside conveys the toner scraped off by the cleaning blade 79 to a toner collection box (not shown).

16 is a transfer charger provided at a position facing the transfer section 160; 60 is a transfer belt whose opening is located at a position opposite to the roller 72 in the wedge-shaped cross-sectional space between the transfer belt 71 and the photosensitive drum IO; This is a paper charger arranged to face 71.

After the development by the developer 43 containing the third color toner on the photoreceptor drum 10 is started as described above, the registration roller 53 is operated, the transfer belt device 70 is pressed, and the discharge wire of the paper charger 60 is activated. High voltage is applied almost simultaneously to both.

As a result, the paper charger 60 performs corona discharge toward the transfer paper fed one by one from the transfer material supply device, and charges the transfer paper to the same polarity as the toner on the photoreceptor drum IO.

The paper charger 60 efficiently and reliably charges the roller 72, which is close to the ground, as a counter electrode, and also charges the transfer portion 1
Since it is provided very close to the transfer belt 60, there is little decrease in charge during conveyance, and the transfer paper can be firmly attracted and held on the transfer belt 71 and conveyed to the transfer section 160.

When the leading edge of the transfer paper reaches the transfer section 160, the transfer belt 7
1, the transfer paper is pressed against the photoreceptor drum IO. Then, the transfer charger 16 charges the toner on the photosensitive drum IO with a polarity opposite to that of the toner, and transfers the toner image onto the transfer paper. The transfer paper onto which the toner image has been transferred is further conveyed by the transfer belt 21 to a fixing section (not shown), where the toner image is fixed on the transfer paper by heat welding and then discharged onto an external paper discharge tray. Reference numeral 55 is a separation claw for preventing the transfer paper from accidentally entering upwards.

FIG. 3 is a cross-sectional configuration diagram showing the vicinity of the paper charger 60 in FIG. 1. In the figure, 61 is a back plate of the paper charger 60 made of a stainless steel plate, a surface-treated steel plate, an aluminum plate, etc., which forms a rolled effect and a stable electric field, and its opening 64 faces the transfer bell 71. It is set up like this. 62 is a discharge wire made of tungsten wire with a diameter of 60 to 100 μm. The back plate 61 has the effect of forming a stable electric field during the charging operation of the paper charger 60, stabilizing corona discharge, and preventing unnecessary portions from being charged. During charging operation, a voltage of 5 to 6 KV is applied to the discharge wire 62. At this time, the distance between the discharge wire 62 and the linear back plate 61 is 6
If the distance is not 7 mm or more, spark discharge will occur and charging will not be carried out, which is dangerous. Therefore, in this embodiment, a tape made of polyester resin, for example, is pasted on the inner wall of the back plate 61 on the photoreceptor drum 10 side to form an insulating layer 63, and the discharge wire 62 is connected to the back plate 6.
This is to prevent spark discharge from occurring even if it approaches 1. In addition, the shape of the back plate 61 has a key-shaped cross section, for example, as shown in FIG. 3, so that it is suitable for an installation space with a wedge-shaped cross section. They can be placed very close together.

The paper charger 60 is provided at a position facing the roller 72, and performs corona discharge toward the transfer paper P fed by the registration roller 53, efficiently and reliably using the roller 72, which is close to the grounded state, as a counter electrode. In addition to charging the transfer sheet P, the distance to the transfer unit 160 can be significantly shortened, so that the transfer belt 71 can firmly adsorb and hold the transfer paper P while conveying it. Separability from the photoreceptor drum 10 can also be maintained well at all times.

The structure of the transfer belt 71 used as the transfer means includes, for example, two layers, and the main body has a thickness of 0.5 to . An endless high-resistance sheet with a volume resistance of around 1010 Ωcm made of silicone rubber, polyurethane rubber, butyl rubber, etc., approximately 1 mm thick.The upper layer of this sheet is spray-coated with fluorine thread resin to lower the frictional resistance. It is.

Further, a high voltage having the same polarity as the charging of the toner of the developer is applied to the discharge wire 62 of the paper charger 60 so that the transfer paper P is charged with the same polarity as the toner.

Therefore, until the transfer paper P reaches the transfer unit 160, the toner on the photosensitive drum 10 is attracted to the transfer paper P.
- Therefore, clear copy image quality can be obtained without blurring or blurring of the image.

The application of the above-mentioned high voltage is performed at a linear velocity of movement of the photoreceptor drum 10 of 140 mm/sec and an image width of 300 to 350+n+n.
When the paper thickness is 65 g/m2, the discharge current is controlled to be 20 to 50 μA, and at this time, the current component flowing in the direction of the transfer paper P is 10 to 20 μA when the humidity is high, and 5 to 10 μA when the humidity is low. .

Further, a high voltage having a polarity opposite to that of toner charging is applied to the transfer charger 16 under constant current control when the transfer paper P is conveyed and the leading edge has slightly passed through the transfer section 160. Transfers the toner image. This constant current control is performed by switching control such that, for example, the current is 350 μA in the case of high humidity and 200 μA in the case of low humidity, and charging is performed.

In this manner, the charging current can be changed in accordance with changes in humidity, which is most susceptible, and good adsorption force and transfer efficiency can always be maintained.

On the other hand, the photosensitive drum IO after the transfer is cleaned by a cleaning device 90 which is a cleaning means. The cleaning blade 91 is provided with a toner collection roller 92 that electrostatically collects residual toner, and while a toner image is being formed on the circumferential surface of the photoreceptor drum 10, the cleaning blade 91 is in a retracted state, and the cleaning blade 91 is in a retracted state when the transfer is completed. Cleaning is performed by pressing against the body drum 10. Also, the cleaning device 90
A static elimination lamp 93 is provided on the upstream side of the
4 is located, and the static elimination lamp 93 is connected to the photoreceptor drum 10.
Static electricity is removed to a state where it is easy to remove residual toner on the peripheral surface, and static electricity removal 4
The lamp 94 uniformly eliminates static electricity from the cleaned circumferential surface of the photosensitive drum 10 so that uniform charging is performed. Furthermore, a toner conveying pipe 95 having a toner conveying screw made of a flexible material is provided at the bottom of the cleaning device 90, and conveys the waste toner collected by cleaning to a toner collecting box (not shown). The photosensitive drum IO that has been cleaned begins the next image forming process.

In the above-described color image forming apparatus shown in FIG. 1, the image forming means is located at the peripheral edge of the photosensitive drum 10 in the arrangement relationship shown in FIG. 4. Then, as shown in the time chart of FIG. 5, sequence control is performed by a control section provided in the main body of the apparatus, and a color image is formed.

〔Effect of the invention〕

According to the present invention, with the configuration as described above, the paper charger of the transfer belt device can be provided extremely close to the transfer section. Therefore, the transfer belt of this device has excellent suction and conveying power for the transfer paper even in a high humidity environment, and it is possible to provide a color image forming device that always has excellent paper passing performance and toner image transfer performance. It became.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing the structure of an embodiment of the color image forming apparatus of the present invention, FIG. 2 is a cross-sectional view showing the developing device shown in FIG. 1, and FIG. FIG. 4 is an explanatory diagram showing the arrangement relationship of each equipment in the image forming apparatus, FIG. 5 is a time chart of image formation performed in the above arrangement relationship, and FIG. 6 is a conventional electrophotographic copying machine. FIG. 7 is a schematic cross-sectional diagram showing an embodiment of a conventional transfer belt device.

Claims (1)

[Claims] A plurality of developing devices with different toner colors are arranged around the periphery of the rotating image carrier, and the developing devices sequentially develop the toner image, and after superimposing the toner image on the image carrier, a transfer belt device transfers the toner image to the transfer material. In a color image forming apparatus that performs image transfer, a paper charger is provided in a wedge-shaped space formed by the image carrier and the belt, and an opening of the paper charger is disposed to face the belt. A color image forming device characterized by: