JP2914531B2 - Multicolor image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multicolor image forming apparatus for forming a multicolor image by one rotation of a photosensitive member.

[0002]

2. Description of the Related Art There are various types of multi-color image forming apparatuses using electrophotographic technology. One of them is to form a toner image on a photoreceptor for each color and record the toner image of each color. 2. Description of the Related Art There is an image forming apparatus that forms a multicolor image by sequentially superimposing and transferring images on paper. In this case, a charger, an exposure unit, a plurality of developing machines, a transfer unit, and a cleaning device corresponding to each color are arranged around a drum-shaped photoconductor, and charging, exposure, and development are performed every rotation of the photoconductor. , Transfer and cleaning are repeated. As a result, the toner image of each color is sequentially superimposed and transferred onto the recording paper for each rotation of the photoconductor, thereby forming a multicolor image.

There is also a multi-color image forming apparatus of a single transfer method in which a toner image of each color is formed on a drum-shaped photosensitive member so as to be superimposed every rotation, and a multi-color image is formed on recording paper by one transfer. Are known.

However, in the multi-color image forming apparatus of the single transfer method, since the photosensitive member must be rotated by the required number of colors, the time required for obtaining the final multi-color image becomes longer. There is.

To solve this problem, Japanese Patent Laid-Open Publication No.
As disclosed in Japanese Patent Publication No. 73883, a plurality of recording units including a charger, an exposure optical system, and a developing device are arranged around a drum-shaped photoconductor, and a toner image of each color is formed during one rotation of the photoconductor. A multicolor image forming apparatus has been proposed in which a toner image of each color is formed on a photoreceptor and transferred onto recording paper in a single transfer step.

[0006]

In the multi-color image forming apparatus of the single transfer method described in the above-mentioned publication, when the development is performed in the second and subsequent developing machines, the image is formed on the photosensitive member by the preceding developing machine. The charged toner image and the developing process are performed again on the toner image.

The toner image on the photoreceptor is only weakly adhered to the surface of the photoreceptor by electrostatic force or mechanical adhesive force. The formed toner image is disturbed. For example, during image formation, the surface of the photoreceptor is negatively charged by a charger, and a negative electrostatic latent image is formed by exposure. Reversal development is performed with a bias applied to the negative electrostatic latent image, and toner having a negative charge adheres to the exposed portion. In the next step, negative charging is performed again. At this time, the toner having the negative charge is affected by the negative electric field of the charger, and the toner image formed in the previous step is disturbed. Also, the toner image may be affected by the ion wind from the charger.

In the next development step, the developer comes into contact with the toner image formed in the previous step, so that the toner image is scraped off by the developer and is again disturbed. Further, since the scraped toner is mixed with the developer and collected in the developing device, a color mixture of the toner occurs. For this reason, there is a disadvantage that color reproducibility is deteriorated.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and prevents a toner image from being disturbed at the time of recharging or development by increasing the adhesion of toner to a photosensitive member. The purpose is to do.

[0010]

A multicolor image forming apparatus according to the present invention comprises a charger, an exposure device, and a developing device along the surface of a photoreceptor, respectively. And a plurality of image recording units forming the same are sequentially arranged, and at least one of the second and subsequent image recording units upstream of the charger or at least one between the charger and the developing device. An electric field applying means for applying an electric field having the same polarity as the electric charge of the toner image formed by the preceding image recording section is provided.

[0011]

In the present invention, when the toner image formed by the preceding image recording section reaches the subsequent image recording section,
At least one of the upstream side of the charger and the portion between the charger and the developing device is charged with the electric charge of the toner image by the electric field applying means.
An electric field of the same polarity is applied. Due to this electric field, the toner is pressed against the photoconductor by electrostatic force, and strongly adheres to the surface of the photoconductor. As a result, even when an electrostatic or mechanical external force is applied to the toner image in a charger or a developing machine of a subsequent image recording unit, the toner image moves on the surface of the photoreceptor or is exposed to light. It is less likely to be detached from the body.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The features of the present invention will be specifically described below based on embodiments with reference to the drawings.

FIG. 1 is a side view showing an embodiment of the multicolor image forming apparatus of the present invention.

The multicolor image forming apparatus includes an upper image forming section 1
And a lower sheet feeder 2. Image forming unit 1
, The belt-shaped photoconductor 3 is disposed vertically around the drive roller 4a, the idler rollers 4b to 4e, and the like. The photoreceptor 3 is driven to rotate in the direction of arrow A by the driving roller 4a. The photoreceptor 3 has a conductive layer, a charge generation layer, and a charge transfer layer on a 100 μm substrate formed of, for example, polyethylene terephthalate resin.
It is formed with a thickness of μm. The photoconductor 3 is biased at, for example, -500 to -1000V.
Around the photosensitive member 3, a first image recording unit 5, a second image recording unit 6, a third image recording unit 7, a fourth image recording unit 8, a pre-transfer corotron 9, a development density sensor 10, a light guide A section 11, a transfer section 12, a pre-cleaning corotron 13, a cleaning device 14, and a ground strip 15 are arranged. Components constituting these image recording units and the like are arranged along a substantially vertical surface of the photoconductor 3. Furthermore,
Inside the lower end of the photoconductor 3, a static elimination lamp 16 that irradiates the photoconductor 3 from inside before and after the transfer unit 12 is arranged.

The transfer section 12 includes a transfer corotron 12a.
And a peeling corotron 12b, and is arranged at the lowermost end of the vertically arranged photosensitive member 3 so that the sheet conveying direction is substantially horizontal. In addition, adjacent to the transfer unit 12, the sheet conveying device 17 and the conveying roller 18
And a transport belt 20 that transports the recording paper after the transfer to the fixing device 19 is provided on the paper discharge side.

The first image recording section 5 includes a first charger 2
1. Laser light source (not shown), rotary polygon mirror 22a irradiated with laser light, motor 22b for rotationally driving this rotary polygon mirror 22a, lenses 22c, 22d, mirrors 22e, 22
f, etc., the first exposure device 22 and the first developing device 24
Etc. are provided. The second image recording unit 6 includes a second charger 25 and a second exposure device 2 including a light emitting diode array.
6, a first electric field applying device 27, a second developing device 28, and the like. Similarly, the third and fourth image recording units 7 and 8 also have third and fourth chargers 29 and 33, third and fourth exposure devices 30,
34, second and third electric field applying devices 31, 35, third and fourth
Developing machines 32 and 36 are provided.

The first, second, third, and fourth image recording units 5, 6, 7, and 8 respectively store, for example, black,
Each color image is formed on the photoreceptor 3 by using the red, green, and blue toners. In addition, each electric field applying device 27, 3
Numerals 1 and 35 apply an electric field to the toner on the photoconductor 3 on the upstream side of each of the developing units 28, 32 and 36 in each of the image recording units 6, 7, and 8.

FIG. 2A shows an example of the configuration of the electric field applying device.
(B). FIG. 3A is a cross-sectional view taken along line II of FIG. Since the electric field applying devices 27, 31, and 35 have the same structure, the first electric field applying device 27 will be described as an example in common.

The electric field applying device 27 includes an electrode roller 27a and a backup roller 27b which are arranged in parallel and close to each other with a certain gap. Each roller 27a,
Insulating guide rollers 27e and 27f that are in contact with each other are attached to both ends of the shafts 27c and 27d of the photoconductor 27b.
Is maintained at a constant distance, for example, 0.2 to 1.0 mm. The electrode roller 27a and the shaft 27c are made of a conductive material, and a negative high voltage of about -500 V is applied to the electrode roller 27a from the power supply 27g via the shaft 27c, for example. The reason why the negative high voltage is applied is to form an electric field having the same polarity as the charge of the toner and press the toner against the photoconductor 3. In addition, the backup roller 27
b and the shaft 27d are also made of a conductive material, and the backup roller 27b is grounded via the shaft 27d.

The final developing density is detected by the developing density sensor 10, and the developing conditions in each of the image recording units 5, 6, 7, and 8 are adjusted so that an appropriate density is obtained.

Each of the developing units 24, 28, 32 and 36 has
Each is provided with a developing roller 24a, 28a, 32a, 36a and a backup roller 24b, 28b, 32b, 36b. Second, third, fourth developing machines 28, 32, 3
No. 6, the toner image formed on the photoreceptor 3 by the preceding developing machine must not be disturbed. For example, the moving speed of the photoreceptor 3 and the developing rolls 28a, 32
A magnetic brush developing method is adopted in which the peripheral surface speeds of a and a are matched.

The sheet feeding section 2 includes an intermediate tray 41, sheet feeding trays 42 and 43, a large capacity tray 44, and a sheet reversing section 4 having sheet feeding devices 37, 38, 39 and 40, respectively.
5 and the like are arranged. The intermediate tray 41 has a switching claw device 4 having a plurality of switching claws 46a, 46b, 46c.
6 are provided.

Next, the operation of the above-described multi-color image forming apparatus will be described with reference to an example of forming a two-color image of red and black.

In this case, the first and second image recording units 5
6 is enabled, and the third and fourth image recording units 7 and 8 are disabled. The switching between the operation and the non-operation is performed by, for example, the first and second chargers 21 and 25, the first charger
And second exposure devices 22, 26, first and second developing machines 2
This is performed by applying a predetermined operating voltage or a bias voltage to only 4, 28.

The photoreceptor 3, which is driven to rotate in the direction of arrow A by the driving roller 4a, is first uniformly charged by the first charger 21 in the first image recording section 5, as shown in FIG. You. As a result, the surface potential of the photoconductor 3 becomes, for example, _VP (where _VP is a negative value).

Next, in the first exposure device 22, the light L _K from the laser modulated by the signal corresponding to the black of the image.
The surface of the photosensitive member 3 is exposed, the potential of the exposed portion, for example, V _R (where, V _R is a negative value) decreases to (see FIG. (B)).

Next, the exposed portion advances to the first developing device 24, where it is developed with black toner T _K (see FIG. 3C). After this development, the surface potential of the black image portion remains low.

Next, the black developing portion advances to the second image recording section 6, where it is charged again by the second charger 25,
The surface potential of the rises to near V _P (see FIG. (D)).

Next, in the second exposure device 26, the surface of the photoreceptor 3 is exposed by light L _R from the light emitting diode array modulated by a signal corresponding to the red color of the image, and the potential of the exposed portion becomes V _R. (See FIG. 3E).

Next, the exposed portion proceeds to the first electric field applying device 27, where the previously formed black toner T having a negative charge is formed.
A negative electric field of about −500 to −2500 V / mm is applied to _K. The intensity of this electric field is selected to be such that the toner is polarized, and as shown in FIG. 4, the black toner T _K having a negative charge is electrostatically repelled by the electric field so that Pressed to the side. Therefore, the adhesion of the black toner T _K to the photoconductor 3 increases.

Next, the exposed portion is advanced to the second developer unit 28, where it is developed by a red toner T _R (FIG. (F)). After this red development, the surface potential of the red image portion remains low. At this time, the developer containing red toner T _R with respect to the black toner T _K is in contact, as described above,
Since the black toner T _K is stably attached to the photoconductor 3, the image of the black toner T _K is not disturbed. Further, a black toner T _K is scraped off the red developer, the second developer unit 28
It will not be collected inside. This prevents color mixing.

The photosensitive member 3 proceeds further and passes through the third and fourth image recording sections 7 and 8, but since these image recording sections 7 and 8 are inoperative, the toner image of each color is not affected. I do not receive.

Next, the charge of the toner image is adjusted by the pre-transfer corotron 9 and the charge removing lamp 16 to make the toner image suitable for transfer. In this case, in the present embodiment, since the toner image is more strongly adhered to the photoconductor 3 than usual, the pre-transfer corotron 9 and the discharging lamp 16 are used to reliably discharge the toner. The charging state is adjusted so that the charging polarity of the toner is substantially uniformly negative.

When the toner image of each color advances to the transfer unit 12, the recording paper is conveyed from any of the trays 41 to 44 of the paper supply unit 2 by any of the paper supply devices 37 to 40 in synchronization with the transfer. The sheet is fed to the image forming unit 1 side along B, and further conveyed by the sheet conveying device 17 and the conveying roller 18 to contact the surface of the photoconductor 3.

In the transfer section 12, the toner image of each color is transferred from the surface of the photoreceptor 3 to the recording paper by the electric field from the transfer corotron 12a. The recording paper after the transfer is separated from the photoreceptor 3 by the separation corotron 12b, and the transfer belt 20
Is carried to the fixing device 19, and the toner image is fixed on the recording paper.

The recording paper after fixing advances in the direction of arrow C, for example, and is directly discharged out of the apparatus by the transport roller 47.

The toner remaining on the recording paper after the transfer is
After the charge state is adjusted by the charge removing lamp 16 and the pre-cleaning corotron 13, the charge is removed by the cleaning device 14. Further, the charge remaining on the photoreceptor 3 is discharged through the ground strip 15 to prepare for the next image forming cycle.

As described above, one multicolor image recording sheet is output by one rotation of the photoconductor 3, so that a multicolor image can be obtained in a short time.

In the case of double-sided copying, the recording paper after fixing advances in the direction of arrow D, is conveyed to the paper reversing unit 45 of the paper feeding unit 2 by the conveying roller 48, and is temporarily moved by the reversing roller 49 in the direction of arrow E. , The rotation of the reversing roller 49 is reversed, the transport direction of the recording paper is reversed in the direction of arrow F, and the recording paper is stored in the intermediate tray 41 with the image surface facing upward. At this time, the recording paper is stored in the intermediate tray 41 from an appropriate position by changing the posture of each switching claw 46a, 46b, 46c of the switching claw device 46 according to the size of the recording paper. The recording paper is sent again to the transfer unit 12 of the image forming unit 1 by the paper feeding device 37, and an image on the back surface of the recording paper is formed. In the case of double-sided printing, a toner image is naturally formed in the image forming unit 1 for each side.

In the above-described embodiment, the case where the disturbance of the toner image at the time of development is prevented has been described. Next, another embodiment of the present invention for preventing the disturbance of the toner image at the time of recharging will be described. This will be described with reference to FIG. In FIG. 5, members and the like corresponding to those in the embodiment shown in FIG. 1 are denoted by the same reference numerals, and redundant description will be omitted.

In the embodiment shown in FIG.
The first to third chargers are located upstream of the chargers 25, 29, and 33, respectively.
Electric field applying devices 27, 31, and 35 are provided. The configuration of each electric field applying device is the same as that described above with reference to FIG.

In the embodiment shown in FIG.
First, in the first image recording unit 5, the first charger 21
Is charged uniformly. Next, in the first exposure device 22, the surface of the photoconductor 3 is exposed to light corresponding to the black of the image to form an electrostatic latent image. Next, the electrostatic latent image proceeds to the first developing device 24, where it is developed with black toner.

Next, the black developing portion is the first electric field applying device 2
Then, the process proceeds to step 7, where the previously formed black toner T _K having a negative charge is formed.
, A negative electric field of about −500 to −2500 V / mm is applied. This electric field increases the adhesion of the black toner T _K to the drum-shaped photoconductor 3 as described above.

Next, the black developing portion advances to the second image recording section 6, where it is charged again by the second charger 25,
Surface potential rises. At this time, the force due to the electric field is applied to the black toner T _K, a black toner T _K is not the toner image is disturbed because the adhered strongly to the photosensitive member 3.
Further, the ion image from the second charger 25 does not affect the toner image.

Next, in the second exposure device 26, the surface of the photoconductor 3 is exposed to light corresponding to the red color of the image, and an electrostatic latent image is formed.

Next, this electrostatic latent image portion is
8 and is developed with red toner. At this time, the developer containing red toner T _R with respect to the black toner T _K is in contact, as described above, since the black toner T _K is stably adhered to the photosensitive member 3, the black toner The image due to T _K is not disturbed. Further, it is possible to prevent the black toner T _{K from} being scraped off by the red developer and being collected in the second developing device 28. This prevents color mixing.

The subsequent operation is the same as that of the embodiment shown in FIG. 1, and the description is omitted.

In the above-described embodiment, the electric field applying device is provided upstream of the developing device or upstream of the charging device.
Electric field applying devices may be provided on both the upstream side of the developing device and the upstream side of the charging device.

In the above embodiment, only the two colors of red and black have been described. However, an image may be formed in any combination of the four colors of black, red, green and blue or in a single color. it can. Furthermore, the colors are not limited to the above four colors, but black, yellow,
Magenta or system can be used, and in this case, full-color reproduction can be performed.

Further, the number of image recording units is not limited to four, and the present invention can be applied to two or more image recording units.

[0051]

As described above, according to the present invention,
In the second and subsequent image recording units, since an electric field is applied to the developed toner immediately before the developing process or the recharging process, the toner is pressed against the photoconductor by electrostatic force,
Adhesion to the photoreceptor increases. Therefore, the toner image does not disturb even if the developer contacts the toner image formed in the previous image recording unit or receives the charging process. Further, since the toner does not mix with the toner of another color, color mixing is prevented. This allows
The quality of the finally obtained multicolor image is improved.

[Brief description of the drawings]

FIG. 1 is a side view showing an embodiment of a multicolor image forming apparatus of the present invention.

FIGS. 2A and 2B are a main part sectional view and a main part plan view of an electric field applying device used in the multicolor image forming apparatus shown in FIG.

FIG. 3 is an explanatory diagram illustrating a process of forming a multicolor image.

FIG. 4 is an explanatory view showing the operation of the electric field applying device.

FIG. 5 is a side view showing another embodiment of the multicolor image forming apparatus of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image forming part 2 Paper feed part 3 Photoconductor 4a Drive roller 4b-4e Idler roller 5-8 Image recording part 9 Pretransfer corotron 10 Development density sensor 11 Light guide part 12 Transfer part 12a Transfer corotron 12b Peeling corotron 13 Precleaning Corotron 14 Cleaning device 15 Ground strip 16 Static elimination lamp 17 Paper transport device 18 Transport roller 19 Fixing device 20 Transport belt 21, 25, 29, 33 Charger 22, 26, 30, 34 Exposure device 22a Rotating polygon mirror 22b Motor 22c, 22d lens 22e, 22f mirror 24, 28, 32, 36 developing machine 24a, 28a, 32a, 36a developing roll 24b, 28b, 32b, 36b backup roller 27, 31, 35 electric field applying device 27a electrode roller 27b back Ppurora 27c, 27d shaft 27e, 27f guide roller 27g Power 37-40 paper feeding device 41 to 44 trays 45 sheet inverting section 46 switching claw device 46a, 46b, 46c switching claw 47, 48 transport rollers 49 reversing rollers

──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Shuji Iseki 2274 Hongo, Fuji Xerox Co., Ltd., Ebina City, Kanagawa Prefecture (72) Inventor Hidefumi Saikai 2274 Hongo, Hongo, Ebina City, Kanagawa Prefecture References JP-A-63-292158 (JP, A) JP-A-62-10670 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G03G 13/01 G03G 15/01- 15/01 117

Claims (1)

(57) [Claims] 1. A plurality of image recording units each including a charger, an exposure device, and a developing device and forming toner images of different colors on the photoconductor are sequentially arranged along the surface of the photoconductor, The charge of the toner image formed by the preceding image recording unit on the upstream side of the charger of at least one image recording unit of the second and subsequent image recording units, or at least one between the charger and the developing unit. A multicolor image forming apparatus provided with an electric field applying means for applying an electric field having the same polarity as that of the multicolor image forming apparatus.