JPH1184912A - Method for forming image - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the soiling of a transfer electrode and a guide member, caused by scattering of toner stuck on a non-image forming area, to assure an excellent transferring performance, and to improve the separating performance of transfer paper from a photoreceptor, by a method for forming the image applying reversal developing system. SOLUTION: As for the method of the image forming by electrifying a surface of the organic photoreceptor 31, forming the latent image on the organic photoreceptor 31 in applying photoirragiation on the image by image exposing means, turning the latent image to the toner image in applying reversal development by developing means 33, transferring the toner image on the transfer paper in simultaneously performing the corona discharge by the transfer electrode 344 from the rear side of the transported transfer paper and discharge exposing processing by discharge exposing means 39, and simultaneously discharging the surface of the organic photoreceptor 31, the discharge exposing means 39 performs the discharge exposure only on the image forming area by the image exposing means from the rear side of the transfer paper P.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an electrophotographic copying machine,
The present invention relates to an image forming apparatus such as a printer and a facsimile, and more particularly to an image forming method for forming an image by a reversal developing method of a digital image forming method.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus, the surface of an organic photoreceptor having a photoconductive material layer provided on an aluminum substrate is uniformly charged by a charger, and an image is irradiated on the surface of the photoreceptor by light irradiation. An electrostatic latent image is formed. Next, the electrostatic latent image on the surface of the photoreceptor is developed by a developer by passing through a development area to form a toner image. The toner image is transferred to transfer paper by a transfer device, and the transfer paper is separated from the photoconductor by a separator and fixed by a fixing device. The residual toner is removed from the surface of the photoreceptor after the transfer by the cleaning device, and is used for the next image formation.

In the above-described conventional image forming apparatus, in order to improve the transfer efficiency, a toner image is exposed to lower the potential on the surface of a photoreceptor. That is, in the case of the analog-type regular developing method, the latent image potential on the surface of the photoconductor and the polarity of the charge of the toner are opposite to each other. Strongly adheres to photoconductor surface. For this reason, the surface of the photoreceptor is exposed before or at the time of transfer to reduce the latent image potential on the surface of the photoreceptor, and the transferability is improved by reducing the Coulomb force acting on the toner and the surface of the photoreceptor.

On the other hand, in the case of the digital reversal developing method, since the latent image potential on the surface of the photoconductor and the charge of the toner have the same polarity, a decrease in the transfer rate due to the Coulomb force between the surface of the photoconductor and the toner. Although this does not occur, the transfer paper strongly adheres to the surface of the photoreceptor due to the high potential of the non-image portion, and the transfer paper cannot be separated from the surface of the photoreceptor. For this reason, it has been practiced to reduce the potential of the non-image area by exposing before or during transfer to eliminate the Coulomb force between the transfer sheet and the photoreceptor surface, thereby improving the separation property of the transfer sheet.

[0005]

The inventors of the present invention have conducted the above-described reversal development method and the transfer, and at the same time, performed the charge erasing exposure to form a large number of images. It has been found that there is a problem that the toner adheres and becomes contaminated, resulting in poor transfer and stain on the back surface of the transfer paper.

That is, as shown in the timing chart of FIG. 2, the charge-removal exposure for transfer is started at the same time as the rotation of the photosensitive member, and is always turned on during image formation. This is preferable in the normal development method because the potential of the surface of the photoconductor can always be reduced by always lighting the photoconductor, and the control signal for the rotation drive of the photoconductor is used for the lighting control of the static elimination exposure. This makes the control easier.

However, in the reversal developing method, charging is started after the driving rotation of the photoconductor is started, and the driving rotation of the photoconductor is stopped after the charging is completed. Uncharged areas are not charged, and weakly charged uncharged areas occur due to the residual potential. In the non-charged area, toner hardly adheres in the case of the regular developing method, and even if developed, the toner and the surface of the photoreceptor are opposite in polarity, so that they do not scatter during image formation and cause trouble. Not something. However, when the reversal developing method is applied, a large amount of toner is developed and adheres, and the polarity of the toner and the surface of the photoconductor is the same. It is easy to fly.

When the non-charged area to which the toner adheres is subjected to static elimination exposure at the transfer section, as shown in FIG. 3, the potential change due to the static elimination exposure of the charged area near the charged area of the non-charged area. Due to the decrease, the lines of electric force act to scatter the toner, adhere to the transfer pole and the like, and cause transfer failure and transfer paper stain due to contamination.

Further, as shown in the explanatory diagram of the potential change in FIG. 4, the same effect as described above also applies to the patch image formed for adjusting the toner density, which causes the transfer pole to be contaminated by toner scattering. I have.

[0010]

Means for Solving the Problems A first invention of the present invention is:
A surface of an organic photoreceptor having a photoconductive material layer provided on an aluminum substrate is charged, and an image is exposed to light by an image exposing means to form a latent image on the surface of the organic photoreceptor. The toner image is reverse-developed to form a toner image, and the corona discharge by the transfer pole and the charge-removal exposure process by the charge-removal exposure unit are simultaneously performed from the back surface of the transferred transfer paper to transfer the toner image to the transfer paper, and the surface of the organic photoreceptor is transferred. In the image forming method for removing static electricity, the static elimination exposure unit removes and exposes only the image forming area by the image exposure unit from the back surface of the transfer paper.

According to a second aspect of the present invention, there is provided the image forming method according to the first aspect, wherein the transfer pole and the charge removing exposure means are simultaneously turned on and off.

A third aspect of the present invention is the image forming method according to the second aspect, wherein the on / off control is performed based on the same signal.

According to a fourth aspect of the present invention, the signal is a signal capable of specifying a position of a transfer sheet.
An image forming method according to the invention.

According to a fifth aspect of the present invention, there is provided the image forming apparatus according to the fourth aspect, wherein the signals capable of specifying the position of the transfer sheet are a leading edge detection signal and a trailing edge detection signal of the transfer sheet. Is the way.

[0015]

In the reversal developing method of the digital image forming method,
Contamination of the transfer pole and transfer guide member due to scattering of toner attached to the non-image forming area by exposing only the developed image forming area from the back side of the transfer paper in the transfer section in synchronization with the transfer by the charge exposing and exposing means. And the transferability of the transfer paper from the photoreceptor can be improved.

[0016]

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

Prior to the description of the embodiments of each invention, the configuration of each device and its operation will be described.

FIG. 5 shows a digital image forming apparatus according to the present invention. The apparatus includes an image reading section 10, a laser writing section 20, an image forming section 30, a sheet feeding section 40, a digital image processing section 50, and an image processing apparatus. It comprises a storage unit 60.

The image reading section 10 includes a first mirror unit 1 having a rod-shaped illumination lamp 11A and a mirror 11B.
And an optical unit including a second mirror unit 12 in which a pair of mirrors 12A and 12B are arranged to face each other. The parallel movement and 1/1 of the second mirror unit 12 with respect to the first mirror unit 11
The image is exposed and scanned by the follow-up movement at the speed of 2, and the image is formed on the image pickup device 15 via the projection lens 14, and the photoelectrically converted electric signal is subjected to image processing by an image processing unit (not shown). Is temporarily stored in the memory of the image storage unit 60.

Next, when the image signal is input to a laser writing section (image exposure means) 20, a laser beam generated from a semiconductor laser (not shown)
A drum-shaped photosensitive drum which is rotationally scanned by a polygon mirror 22 rotated by 1 and is previously charged to a constant potential by a charger 32 through an exposure optical system including an fθ lens 23, mirrors 24, 27, 25 and a cylindrical lens 26. An electrostatic latent image of a document image is formed by scanning and exposing the surface of the photoconductor of the body 31. Accordingly, an electrostatic latent image of a document image is formed on the peripheral surface of the photoconductor 31 by the main scanning with the laser beam and the sub-scanning accompanying the rotation of the photoconductor 31. This latent image is reversely developed by a developer carried by a developing sleeve 33A of a developing device (developing means) 33 to be a toner image.

On the other hand, transfer paper P of a designated size is supplied from a paper feed cassette 41 loaded in the paper feed section 40 to the paper feed cassette 4.
The sheet is unloaded by the operation of one unloading roller 42, and is fed to the image transfer area via the transport roller 43.

The fed transfer paper P is applied to a registration roller 44.
The timing is adjusted to the image forming area on the peripheral surface of the photoreceptor 31, and the sheet is fed to the transfer area synchronously,
The corona charging and the charge elimination exposure are performed by the transfer unit 34, and the toner image is transferred.

The transfer paper P on which the toner image has been transferred
In the photoconductor 31, the charge on the back surface is eliminated by the separator 35.
And is conveyed to the fixing device 37 via the conveying belt 36, where the toner is welded by the nipping and heating of the upper roller 37A and the lower roller 37B, and then discharged from the fixing device 37 via the conveying roller 45. You.

The discharged transfer sheet P is discharged onto a tray 47 via a discharge roller 46.

On the other hand, the photoconductor 31 from which the transfer paper P is separated is
Blade 38A pressed against cleaning device 38
, The residual toner on the surface is removed and cleaned, and then charged again by the charger 32 to start the next image forming process.

In the above-described image forming apparatus, the photosensitive member 31 has an organic photosensitive layer (OPC) on the surface of the aluminum base.
This is a drum-shaped organic photoreceptor having a diameter of 80 mm to which is coated, and is rotated at a linear speed of 280 mm / sec during image formation. A charger 32 for charging the photoconductor 31 is a scorotron charger with a grid, and uniformly charges the photoconductor surface to a charging potential of -750V. A semiconductor laser for forming a latent image of the laser writing unit 20 has an output wavelength of 780 nm and a length of 5 m.
With a laser of W output, pulse width modulation is enabled to a level of 256 gradations of 8 bits. A two-component developer consisting of a negatively charged toner having a weight average particle size of 8.5 μm using a polyester resin as a binder and a carrier having a weight average particle size of 60 μm obtained by applying a resin coating to ferrite is used as a developer. The developing sleeve 33A has a diameter of 4
At 0 mm, the photosensitive drum 31 rotates at a rotation speed of 250 rpm, a developing bias of -600 V is applied between the developing sleeve 33A and the photosensitive member 31, and reversal development of the latent image portion is performed with a developing gap of 500 µm.

The present invention will be specifically described with reference to FIGS. FIG. 6 is a cross-sectional view showing a configuration near a transfer unit and a separator of the image forming apparatus of the present invention. FIG. 7 is a block diagram of the control means of the present invention.

The transfer casing 34 and the shield casing 341 of the separator 35 are held and positioned by a lower support frame 342, and are detachable by sliding in a direction perpendicular to the plane of the drawing. A paper guide (transfer guide member) 343 is provided above the shield casing 341. In the shield casing 341, a static elimination exposure unit 39 is provided. The charge removing exposure unit 39 is composed of an LED array arranged along the axial direction of the photoconductor 31.

Below the transfer pole 344, a small opening 391 is formed in the bottom surface of the shield casing 341.
The light beam emitted from the charge removing exposure unit 39 is
The light passes through 91 and is irradiated to the vicinity of the transfer area of the photoconductor 31.

A paper passage detection sensor (hereinafter, referred to as a sensor) PS is provided downstream of the registration roller 44 in the transfer paper transfer.
1 detects the passage of the leading edge and the trailing edge of the transfer paper P conveyed to the transfer area of the photoconductor 31 through the registration roller 44, generates a signal, and sends the signal to the control means 70.

A paper passage detection sensor PS2 is provided upstream of the registration roller 44 in the transfer paper conveyance.
Detecting passage of the leading end of the transfer paper P, the registration roller 44
Controls the timing of rotation and stop. Using the paper passage detection sensor (hereinafter, referred to as a sensor) PS2, the transfer paper P during the conveyance of the transfer paper P by the rotation of the registration roller 44 is used.
Alternatively, a signal may be generated by detecting the passage of the rear end portion and sent to the control means 70.

A transfer paper entering guide plate 48 is provided downstream of the transfer of the transfer paper from the sensor PS1. The transfer paper P is formed between the photosensitive member 31 and the paper guide 343 of the transfer separation section. Feed into the transport path.

The lighting control of the charge exposing means 39 is controlled as shown in FIG. Hereinafter, the lighting control of the charge removing exposure unit 39 will be described with reference to a timing chart shown in FIG.

The driving of the photosensitive member 31 is slightly delayed by the copy start signal and the charging device 32 is slightly delayed by the timer.
, Uniform charging is started. Photoreceptor 3 uniformly charged
An image is radiated on the surface of No. 1 and is reversely developed by the developing device 33 to form a toner image.

Next, the transfer paper P by the transfer pole of the transfer unit 34
The surface of the photoreceptor 31 is subjected to charge removal exposure by the corona charging and the charge removal exposure unit 39 to transfer the toner image, and then the charge removal of the back side of the transfer paper P is performed by the separator 35 to be separated from the photosensitive member 31. You. Reference numeral 351 denotes a separation pole made of a corona discharge wire.

At this time, the discharge exposure means 39 is turned on (O
N), the timing of turning off (OFF) is controlled based on a signal capable of specifying the position of the transfer sheet P as shown in the time chart of FIG. In this case, the timing of the ON / OFF control of the charge eliminating exposure unit 39 is performed in synchronization with the timing of the ON / OFF control of the transfer pole 344 of the transfer device 34.

The timing of the ON control is determined by a timer after a predetermined time by a timer based on a detection signal of the leading end of the transfer paper P by a sensor PS1 provided downstream of the registration roller 44.
By performing the N control, the control is synchronized with the entry of the transfer sheet P, and is controlled to be ON only when the leading end of the transfer sheet P enters the transfer area. In the present embodiment, the sensor P
Although S1 is provided to detect the leading end of the transfer sheet P, the sensor PS1 may not be used if the leading end detection signal of the transfer sheet P is a drive start signal of the registration roller 44.

The timing of the OFF control is such that the trailing end is detected by the sensor PS1, and the OFF control is performed after a predetermined time by a timer based on this signal, thereby synchronizing with the discharge of the transfer paper P, and It is controlled to be turned off at the same time as the trailing end of the transfer paper P is discharged.
The trailing edge detection signal of the transfer sheet P may be used as the trailing edge detection signal of the transfer sheet P based on the drive start signal of the registration roller 44 and the size information of the transfer sheet.

Further, the trailing edge detection signal of the transfer sheet P is determined by a timer for a predetermined time based on the trailing edge detection signal of the transfer sheet P by the registration roller stop control sensor PS2 provided upstream of the registration roller 44. It is also possible to perform the OFF control after the elapse. The sensor PS2 is a sensor PS1
The transfer distance of the transfer paper P from the sensor PS2 to the transfer position is longer than that of the transfer position from the transfer position. Since the time until signal generation for the OFF control of the means 39 can be lengthened, there is an advantage that the timing accuracy of the termination of the charge removal exposure processing is improved particularly when the transfer paper P is transported at a high speed.

By performing the ON / OFF control as described above, only when the transfer paper P exists in the transfer area, that is, only the image forming area on the surface of the corresponding photoconductor 31 is transferred to the transfer paper P.
Of the photosensitive member 31 in the non-image forming area is not performed. Also, at times other than the transfer, the static elimination exposure is turned off, so that the static elimination exposure is not performed on the toner attached to the non-charged area or on the patch image for adjusting the toner density. Thus, problems such as poor transfer due to transfer pole contamination and back surface contamination of the transfer paper P can be solved, and the transfer paper P can be satisfactorily separated from the surface of the photoconductor 31.

The image forming conditions in the present invention were carried out under the following conditions.

Photoconductor linear velocity: 280 mm / s Photoconductor charging potential: −750 V Total charging current: −800 μA Transfer total current: +300 μA Developing sleeve rotation speed: 250 rpm Developing electric field: 550 V Static elimination exposure means (L): LED, 24 V drive Developer (two-component developer): Toner: polyester-based, average particle size 8.5 μm Carrier: resin coating on ferrite, average particle size 60 μm Toner concentration: 6%

[0043]

As described above, according to the image forming method of the present invention, in the reversal developing method of the digital image forming method, only the developed image forming area is subjected to the static elimination exposure from the back surface of the transfer paper. Prevents contamination of transfer poles and transfer guide members due to scattering of toner attached to non-image forming areas,
It is possible to ensure good transferability and to make the transfer paper separable from the photoreceptor good.

[Brief description of the drawings]

FIG. 1 is a timing chart of control in an image forming apparatus of the present invention.

FIG. 2 is a timing chart of control in a conventional image forming apparatus.

FIG. 3 is an explanatory diagram showing a change in potential of a non-charged area due to charge removal exposure.

FIG. 4 is an explanatory diagram showing a potential change due to static elimination exposure of an image.

FIG. 5 is a sectional configuration diagram of the image forming apparatus of the present invention.

FIG. 6 is a cross-sectional view illustrating a configuration near a transfer unit and a separator of the image forming apparatus of the present invention.

FIG. 7 is a block diagram of control means of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 10 image reading unit 20 laser writing unit (image exposure unit) 30 image forming unit 31 photoconductor (organic photoconductor) 32 charger 33 developing unit (developing unit) 34 transfer unit 341 shield casing 342 support frame 343 paper guide (transfer) Guide member) 344 Transfer pole 35 Separator 351 Separation pole 39 Static elimination exposure unit 40 Feed unit 44 Registration roller 48 Transfer paper entry guide plate 70 Control unit PS1, PS2 Paper passage detection sensor (sensor) P Transfer paper -Vb Charge potential- Vz Residual potential when not charged -Vd Residual potential after static elimination exposure -Va Image potential

Claims (5)

[Claims] 1. A surface of an organic photoreceptor having a photoconductive material layer provided on an aluminum substrate is charged, and an image is irradiated with light by an image exposure means to form a latent image on the surface of the organic photoreceptor.
The latent image is reversely developed by a developing unit to form a toner image, and corona discharge by a transfer pole and static elimination exposure processing by a static elimination exposure unit are simultaneously performed from the back surface of the transferred transfer paper to transfer the toner image to the transfer paper. In the image forming method for removing electricity from the surface of the organic photoreceptor, the charge removing and exposing means removes and exposes only the image forming area by the image exposing means from the back surface of the transfer paper. 2. The image forming method according to claim 1, wherein the transfer pole and the charge removing exposure unit are simultaneously turned on and off. 3. The image forming method according to claim 2, wherein the on / off control is performed based on the same signal. 4. The image forming method according to claim 3, wherein the signal is a signal that can specify a position of a transfer sheet. 5. A signal that can specify the position of the transfer sheet is:
5. The image forming method according to claim 4, wherein the signal is a leading edge detection signal and a trailing edge detection signal of the transfer paper.