JPH0486883A - Image forming device - Google Patents

Abstract

PURPOSE:To surely prevent toner from being accumulated in a toner image nonpatterning means and to prolong the life of the device by providing a mode wherein the toner accumulated in the transfer remaining nonpatterning member is discharged to an image carrier and applying an AC bias to the toner image nonpatterning means. CONSTITUTION:A toner image and an electrostatic latent image slightly remain on the surface of a photosensitive drum 1 after transfer and are carried to the transfer remaining toner nonpatterning means 2. A DC bias having the opposite polarity from the toner is applied to a brush 2a so as to attract the transfer remaining toner temporarily and inject charges. Much of toner attracted temporarily to the brush 2a resticks on a drum 1, but the rest of the toner can not restick and is accumulated in the brush 2a gradually. Consequently, discharging operation (discharge mode) for the toner accumulated in the brush 2a is performed during print start operation and/or end operation, etc. In this discharge mode, a DC bias is applied and then even toner entering the brush 2a deeply is discharged to reduce the accumulation in the brush 2a, thereby prolonging the life of the device.

Description

Detailed Description of the Invention [Objective of the Invention] (Industrial Application Field) The present invention forms an electrostatic latent image on an image bearing member such as a photoreceptor, develops this electrostatic latent image, and prints a sheet of paper, etc. The present invention relates to a recording device for recording on a transfer material.

(Prior Art) As this type of recording device, electrophotographic devices, electrostatic printers, and the like are known. In these recording devices, after forming an electrostatic latent image on a photoreceptor, a developer is electrostatically attached to the electrostatic latent image to form a developer image, and then the developer image is transferred to paper. Recording is done by transcription.

Furthermore, since the electrostatic latent image and developer that has not been transferred remain on the photoconductor after transfer, the remaining developer is removed by a cleaning device, and then the electrostatic latent image is removed by a static eliminator. It is being removed.

Incidentally, in recent years, there has been a demand for downsizing of devices, and for example, Japanese Patent Laid-Open No. 11538/1983 discloses a method of downsizing the device by using one device as both a developing device and a cleaning device. ing. In this method, in one developing device, the electrostatic latent image is developed when the photosensitive drum passes through it for the first time, and then the residual image after the transfer is cleaned by passing through the developing device a second time. ing. However, in this conventional method, the residual image is removed when the photosensitive drum passes the developing device for the 20th time, so the recording speed is halved and the circumference of the photosensitive drum is removed. There is a problem in that a recording area larger than the entire surface cannot be obtained, and the photosensitive drum must necessarily be relatively large in size, making it impossible to make the device sufficiently small.

On the other hand, U.S. Patent No. 364926 discloses a developing device that simultaneously develops the electrostatic latent image and cleans the developer remaining after the previous transfer when the electrostatic latent image passes for the first time. A method is disclosed which overcomes the speed disadvantage by using the following methods.

(Problem to be Solved by the Invention) However, in this conventional device, the residual image after transfer is left on the photosensitive drum, and then the next charging, formation of an electrostatic latent image, and development are performed on the residual image. become. Therefore, during charging, the remaining latent image and toner image are charged overlappingly, and the next image exposure is performed from above this torch image, which impairs uniform charging and formation of the latent image. However, an afterimage from the above process or a so-called memory image appears superimposed on the next screen, resulting in a disadvantage that the image becomes unclear. This type of development is particularly likely to occur when a solid area (an area where the developer adheres over a wide area) and a residual image such as a character formed in a previous process meet, and often not only the latent image but also the developer Because the developer image cannot be removed sufficiently, the developer image may also remain as an afterimage memory and be transferred to the paper as is.

As described above, conventional recording apparatuses have the problem that sufficient reliability cannot be obtained and often clear images cannot be obtained.

Therefore, as shown in Japanese Patent Publication No. 84-20587, a method has been devised in which the residual toner is removed by applying a brush or the like, and this brush is applied with a bias having a polarity opposite to that of the toner. It is effective when applied. However, when printing was performed continuously, toner accumulated on this brush, causing dirt inside the machine and a decrease in the brush's non-bumping ability.

The present invention was made in view of the above circumstances, and an object of the present invention is to provide a recording device that can obtain clear images even when printing is performed continuously.

[Structure of the Invention] (Means for Solving the Problems) In order to solve the above problems, the present invention provides an electrostatic latent image forming means for forming an electrostatic latent image on an image bearing member, and an electrostatic latent image forming means for forming an electrostatic latent image on an image bearing member. a developer cleaning means for removing the developer remaining on the image carrier while supplying a developer charged to the same polarity as the developer and performing reversal development; and a developer image formed on the image carrier to be transferred. In the image forming apparatus, the image forming apparatus includes a transfer means for transferring onto a member, and a non-patterning means for slidingly contacting the untransferred developer remaining on the image carrier after the transfer and non-patterning the image formed by the untransferred developer. A discharge mode is set in which the developer accumulated in the non-patterning means is reattached to the image carrier. and applying means for applying an AC bias to the non-patterned member when the ejection mode is set by the setting means.

(Function) It has a mode in which the toner accumulated in the transfer residual image non-battering member is discharged onto the image carrier, and in the parenthesis mode, by applying an alternating current bias to the toner image non-blasting means, the toner image is removed. The toner accumulated in the non-battery means can be sufficiently discharged onto the photoreceptor, the toner can be reliably prevented from accumulating on the toner image non-battery means, and the life of the device can be extended.

(Example) The present invention will be described below with reference to an example shown in the drawings.

FIG. 1 shows a recording device according to the present invention, in which a photoreceptor as an image carrier is provided with a recording surface smaller than the area of the image to be recorded (that is, a small diameter) approximately at the center of its main body H. A drum 1 is provided rotatably in the direction of arrow A.

The photoreceptor drum 1 is made of an organic photoreceptor (OPC) type photoconductive material.

Around the photo-recording drum 1, there are disposed a residual toner non-bumping means 2, a static eliminating means 7, a scorotron charger 3, a laser device 4, a developing cleaning device 5, and a transfer roller 6.

The transfer residual toner non-banning means 2 has 10' to 10
It has a brush 2a made of fiber (trade name: Trading Card, Kynor, etc.) having an electrical resistance of 9Ω mark, and is arranged so as to be in sliding contact with the photoreceptor drum 1, and has an electrical resistance of +200 to 120Ω.
A voltage of 0V is applied. Further, the scorotron charger 3 charges the surface of the photoreceptor drum 1 at -450 to
It is designed to be negatively charged approximately uniformly to -800V.

The laser device 4, depending on the image information to be recorded,
A laser beam 8 is irradiated onto the surface of the photoreceptor drum 1 to form an electrostatic latent image in the charged area.

Further, the developer cleaning device 5 has a hopper 9 that stores a so-called one-component developer T that is triboelectrically charged. A developing roller 10 is provided that transports the developer T remaining on the photoreceptor drum 1 and returns it to the hopper 9 .

The developing roller 10 is composed of an electrically conductive surface layer 11 having an electrical resistance of 102 to 108 Ω (maximum), and an elastic layer 12 made of foamed urethane, silicone rubber, EPDM, etc. inside, and has elasticity as a whole. A roller is configured.

The developing roller 10 is triboelectrically charged with the developer T.
An elastic blade 13 made of phosphor bronze, urethane, silicone resin, etc. is pressed to form a thin layer, and the developer T passing through this blade is charged with a negative frictional charge of the same polarity as the photoreceptor drum 1. One to three developer layers are formed.

The surface of the developing roller 10 needs to be selected in consideration of frictional electrification with the developer T and appropriate elasticity and frictional properties. The material of the surface layer 11 is, for example, a mixture of urethane resin and 10 to 30% by weight of conductive carbon. Furthermore, a bias power supply 14 is connected to the developing roller 10,
It is electrically connected to the surface layer 11. Thereby, a predetermined developing bias is applied during development and cleaning. Hopper 9
A sponge-like developer conveying roller 15 is provided inside the hopper 9, and plays the role of preventing agglomeration of the developer T in the hopper 9 and conveying and supplying it.

The transfer roller 6 is provided substantially below the photoreceptor drum 1 so as to face the circumferential surface of the photoreceptor drum 1 via the paper conveyance path 16 .

The transfer roller 6 has the same structure as the developing roller 10, but the electrical resistance of the surface layer 11 is 105 to 1010Ω. The transfer roller 6 applies a voltage of 800 to 2000 V to the back surface of the paper P conveyed here to electrostatically attract the toner, thereby transferring the toner image from the photoreceptor drum 1 onto the paper.

This type of contact transfer means exhibits stable transfer characteristics even under high humidity conditions, so it is effective in reducing the amount of developer remaining after transfer and reducing the burden of cleaning, and also reduces paper dust in the transfer paper. Remove it and prevent it from getting mixed into the developer.

The conductive brush 2a of the transfer residual toner removal means 2 is brought into sliding contact with the photoreceptor drum 1 as it rotates, and is connected to a bias power source 23 to which a voltage of 200 to 1500 V is applied to remove the transfer residual on the photoreceptor drum 1. Temporarily adsorbs developer. Since most of the toner remaining after transfer has negative polarity,
Transferred residual toner is attracted to the non-bumping means 2, but some of the transferred residual toner of the fogging toner is positively charged, and these toners pass through without being attracted, but the amount is small and causes a problem. Must not be. - The residual transfer toner trapped in the residual transfer toner non-bumping means 2 may be caused by the applied bias or the resistance of the brush 2a.
A positive charge is injected at a time depending on conditions such as the particle size and resistance of the toner, and is returned to the photosensitive drum 1 by an electric field formed by the brush 2a and the photosensitive drum 1.

As described above, the time it takes for the transferred residual toner to be trapped by the residual transferred toner non-bumping means 2, receive charge injection, and be returned to the photosensitive drum 1 depends on the particle size of the toner,
Due to resistance etc., the distribution will have a certain width. Therefore, the residual toner after transfer is non-battered. In addition, the brush 2a is used to remove residual toner from the transfer.
The mechanical sweeping effect also contributes. but,
Rather than all the toner being returned to the photoreceptor drum 1,
Toner gradually accumulates on the brush 2a.

FIG. 2 shows the structure of the brush 2a.

The toner returned to the photoreceptor drum 1 has a positive polarity that is opposite to the normal polarity, but when the photoreceptor drum 1 is charged by the scorotron charger 3, it is exposed to negative corona and the toner also has negative polarity. Then, it is cleaned in the developing and cleaning device 5.

Next, the resistance of the brush 2a will be described. If the resistance of the brush 2a is too large, the responsiveness of the potential at the tip of the brush 2a will be poor, causing toner adsorption and charge injection to the photosensitive drum 1.
The time constant of the operation to return to
Toner cannot be returned sufficiently to the photoreceptor drum 1, leading to problems such as increased toner accumulation. Furthermore, if the resistance of the brush 2a is too low, bias will leak to the photoreceptor drum 1, causing destruction of the photoreceptor.

Therefore, it is desirable that the resistance of the brush 2a is 10 3 to 10 9 Ω. Further, the photosensitive drum 1 is also positively charged by the brush 2a, but the potential at this time varies depending on the amount of untransferred toner, etc., so the charging device may be a scorotron charger 3 as in this embodiment. desirable.

In this way, since the residual toner after transfer is trapped and swept out in a short cycle, the amount of toner remaining on the brush 2a is very small. However, when printing continuously, the amount of trapped toner gradually accumulates, and when it exceeds the allowable amount, it may scatter, or the brush may suddenly eject a large amount of toner, resulting in image defects. occurs.

Therefore, the developer T adhering to the brush 2a can be disposed above the photoreceptor drum 1 or closer to the developing device from above with respect to the photosensitive drum 1.
This can reduce the risk of objects falling and scattering inside the aircraft.

Below the photosensitive drum 1, the paper P is conveyed through a conveyance path 16.
A paper feed unit 19 is provided for supplying paper to the paper. This paper feeding unit 19 stores a paper P to which an image is to be transferred. A paper feed roller 20 is provided above the paper feed unit 19 and supplies the paper P from the paper feed unit 19 to the transport path 16 by rotation.

The conveying path 16 is provided with a fixing device 21 that fixes the transferred toner image onto the paper P, and fixes the toner image on the paper P using heat and pressure.

Next, the operation of the electronic copying apparatus according to this embodiment will be explained.

The photoreceptor drum 1 is rotated in the direction of arrow A, and the circumferential surface of the photoreceptor drum 1 is charged approximately -450 to 8 by the Scorotron charger 3.
Charge to 00v. Subsequently, this charged area is exposed by irradiating a laser beam 8 from the laser device 4 to form an electrostatic latent image on the surface of the photoreceptor drum 1. The electrostatic latent image is then conveyed to a developing cleaning position facing the developing cleaning device 5. Developer (toner) is supplied from the developing roller 11 of the developing cleaning device 5.
The toner T is sent out and comes into contact with the electrostatic latent image elastically and with a nip width due to deformation, and the toner T is attached to form a toner image. In this case, the toner T adheres to the light irradiation area, resulting in so-called reversal development. The toner T is charged to approximately -5 to 30 μC/g (microcoulombs/gram) due to friction between the blade 13 and the surface layer 11 of the developing roller 10 , and the developing roller 10 has a charge of approximately −150 μC/g.
A voltage of ˜450 μm is applied. The toner image after development is
Next, it is conveyed to the transfer area facing the transfer roller 6. On the other hand, the paper P is fed to the transfer area from the paper feed unit 19 by the rotation of the paper feed roller 20 in synchronization with the rotation of the photosensitive drum 1.

The back surface of the paper P is charged to a positive polarity by the transfer roller 6. Therefore, the toner image on the surface of the photosensitive drum 1 is electrically attracted to the paper P and transferred. Here, the transfer roller 6 is applied with a voltage of 600 to 2000 V to the rotating shaft by a DC power source 23, and is made of silicone resin provided at both ends of the transfer roller 6 mixed with 5 to 40 percent conductive carbon. A voltage is applied to the conductive surface portion of the roller surface having a resistance of 10 5 to 10 9 Ω through the conductive portion. The surface of the transfer roller 6 is preferably made of a material with a smooth surface and low friction in order to make it easier to clean foreign matter such as developer and paper dust that adheres to it. In this example, conductive polyfluoride resin is used. , conductive polyester, etc., and can be cleaned well with a cleaning blade.

In addition, as for the rubber hardness of the entire roller, a flexible one having a rubber hardness of 25 to 50 degrees was found to have a wide tolerance for the pressing force of the transfer roller 6 against the photoreceptor drum 1 according to comparative measurements according to the JIS method.

In a transfer method using a transfer roller, there is no dependence of transfer efficiency on the environment (especially humidity). In corona transfer, the transfer efficiency decreases significantly in a humid environment.

This means that in a recording device that does not have a cleaning device like the one of the present invention, the amount of residual toner after transfer increases rapidly in high humidity conditions, and this is due to poor cleaning in so-called cleanerless recording devices that do not have a cleaning device in the past. The biggest cause.

From the above, the roller transfer method is very effective in cleanerless processes.

By the way, a small amount of the toner image and electrostatic latent image that were not completely transferred remain on the surface of the photoreceptor drum 1 after the transfer. These toner images and electrostatic latent images are conveyed to the transfer residual toner non-battery forming means 2 and are non-batteryized. In the transfer residual toner removal means 2, the brush 2a is brought into contact with the toner image and the electrostatic latent image to apply electrostatic and mechanical force to finely remove the residual toner image so as to make it illegible. Disturb the image that is being held.

The toner T scattered on the surface of the photoreceptor drum 1 is distributed in the form of a sufficiently small mist and no longer contains information as characters or images. The electrostatic latent image remaining on the photoreceptor drum 1 is erased by the static eliminating means (red LED),
Return to the charging process.

Photosensitive drum 1 charged by Scorotron charger 3
After being charged, a static image 71 exposed by the laser device 4 is formed, and reaches the developing cleaning position facing the developing cleaning device 5 again (for the second time). In this case, in the electrostatic latent image formed the second time, the exposed areas (image areas to which toner should adhere) and non-exposed areas (non-image areas) have also been significantly reduced due to roller transfer. almost uniformly, and
Since the residual toner is scattered thinly enough, uneven exposure will not occur. Therefore, even in the second development,
Since the residual potential after exposure becomes uniform, a uniform toner image can be obtained.

Here, as mentioned above, the developing roller 10 is
The developing roller 1
By applying a load of 20 to 150 g/cITl as a line load to the nip and pressing and sliding contact with a speed difference of 1.5 to 4 times, a bump) with a contact width of 1 to 4 mm is generated, and in this nip. Since the residual toner and the toner T on the developing roller 10 are agitated and rubbed, a strong frictional force is generated and the cleaning ability is enhanced. Furthermore, since the developer is formed only from the toner T, no deterioration in image quality such as streaks or shading occurs. Further, in the non-exposed area, since the suction force due to the developing bias is stronger than that of the photosensitive drum 1, the toner T that has been attached to the toner T is successively attracted to the developing cleaning device 5 and collected.

That is, by applying a developing bias of an appropriate value (-150V to -450V in the embodiment) between the residual potential of the exposed area and the potential of the non-exposed area, the developing roller 10 is exposed to light. New toner adheres to the area, and at the same time, residual toner adhering to the non-image area (non-image area) is attracted from there to the developing roller 10 and collected. In this case, since the residual toner is small and has already been dispersed in the form of a small mist in the transfer residual toner non-blasting unit 2, the developing and cleaning device 5 can efficiently collect the residual toner, which may result in poor collection. Never. In this way, the photoreceptor drum 1 is rotated and used overlappingly, and - number of recorded images are obtained.

As the transfer method, it is preferable to use the transfer port 6 as in the embodiment, but even if a corona transfer method is used, there is no problem in practical use.

After development and cleaning, the toner image is transferred to the transfer roller 6.
The paper P is transferred at a position facing the paper P. Thereafter, similar steps are repeated.

In order to temporarily adsorb the residual toner and inject charge,
In the embodiment, a DC bias with a polarity opposite to that of the toner is applied to the brush 2.
is applied to a. Although much of the toner temporarily adsorbed (trapped) on the brush 2a re-adheres to the photoreceptor drum 1, it is conceivable that some of the toner is not completely re-adhered and gradually accumulates on the brush 2a. Therefore, in the embodiment, an operation for starting and/or ending printing, and an operation (discharge mode) for discharging the toner accumulated on the brush 2a when the machine power is turned on are performed. In the ejection mode, it is preferable to apply a bias to actively eject the accumulated toner. For example, it is also effective to apply a bias of -200 to -800 V with the opposite polarity to the bias applied during the printing operation (normal mode), or to gradually change the bias to 0N10FF (DC sweep mode). However, even if such measures are taken, if printing including many areas with high image density is repeatedly performed, toner will accumulate on the brush 2a and toner scattering will occur.

Therefore, when an alternating current bias is applied in the ejection mode, even the toner that has penetrated deep into the brush 2a can be sufficiently ejected, and the accumulation of toner on the brush 2a is drastically reduced. The applied bias at this time may be a combination of alternating current and direct current.

If there is a difference of 100V or more between the DC component of the bias and the photoreceptor potential in ejection mode, charge is injected into the toner.
A considerable amount of toner is ejected.

However, most of the toner accumulated on the brush has a negative polarity that has not received charge injection from the brush, so the photoreceptor surface potential is higher than the DC component of the brush bias in ejection mode. , more efficient discharge is possible. In the example, the DC component is -650V and the AC component is 14V.
00V pi) and a superimposed bias of 1 kHz was applied. At this time, the photoconductor potential when the brush passes is -550V.
(transfer bias is off), and the photoreceptor potential is approximately 100 cm higher than the DC component of the brush bias in the ejection mode, and the toner is sufficiently ejected due to the potential difference and the oscillating electric field of the AC bias. The ejected toner is negatively charged along with the photoreceptor drum 1 by the charger, separated from the photoreceptor by the developer and cleaner 4 (at this time, the developer bias is on), and collected by the developer and cleaner 4. If there is a lot of accumulated toner, one cycle of cleaning operation will not be enough to clean it.
It is desirable that the discharge mode be performed in two or more revolutions of the photoreceptor drum 1 (the above is an example of the AC discharge mode).

In the case of the above method, a positive DC bias is applied in the normal mode, and a bias that is a combination of negative DC and AC is applied in the ejection mode, making the bias power source expensive. Therefore, by turning on the transfer bias in the ejection mode and positively charging the photoreceptor, the accumulated toner can be ejected even if the DC component of the brush bias has a positive polarity. However, in this method, if the discharged toner is not sufficiently cleaned by the developing and cleaning device in one rotation, the transfer roller 6 will attract the toner remaining after cleaning. It is desirable that the transfer roller 6 has a cleaning means. When turning on transfer in ejection mode, it is better to use a non-contact transfer method (for example,
Corotron charger or scorotron charger) is preferable because the transfer means does not get dirty (example 2 of AC discharge mode).

Further, the above-mentioned ejection may be performed at paper intervals. By performing the discharging operation for each print, the toner brush 2a
This prevents toner from accumulating on the toner and prevents toner from scattering.

Images with an image area ratio of approximately 12% were continuously printed to test the occurrence of toner scattering due to brush stains. The ejection conditions are 1) without ejection mode, and when DC ejection mode is used at the start and end of printing (
2), When performing AC discharge mode example 1 (3), example 2
The test was conducted under five conditions: (4), when AC discharge mode Example 2 was performed at paper intervals (5).

FIG. 3 shows this result. As shown in the figure, if the AC discharge mode is adopted, toner scattering will not occur even if 20,000 sheets are printed.

Note that under the conditions (2) to (4), printing was interrupted and ejection was performed every 250 prints (for one power set).

Next, the AC frequency of the bias will be described.

In order to eject toner effectively, it is necessary to apply a certain level of vibration to the toner. However, if the frequency becomes too high, the toner accumulated on the brush cannot follow the changes in the electric field, resulting in insufficient ejection. Brush bias DC+400■ in normal mode, Tenobi 7 in discharge mode
A similar printing test was conducted under the conditions of DC+ 400V and AC 1400Vpp, changing the bias frequency from 10011z to 5 to 11z (AC ejection mode example 2).

Figure 4 shows the results, and the frequency 3001
If it is not more than 1z, the toner may not vibrate due to the electric field,
The ejection effect is insufficient, and plan stains and toner scattering occur. On the other hand, brush stains and toner scattering occurred even at frequencies of 4 kHz or higher. From the above results, the appropriate frequency was approximately 300 Hz to 4 kHz.

In the example, we have explained the case where the brush bias in normal mode is DC, but AC (or AC and DC superimposition) bias is effective also in the memory erasing effect, and the bias in normal mode is AC bias. Good too.

Although the embodiment has been described using the transfer roller 6, the function is the same even if a corona transfer type transfer means is used, and other known transfer means can be used.

In the above embodiment, the non-magnetic component development method was used as the most compact example, but the method is not limited to this, and other known magnetic component brush methods, far plan methods, and cascade methods are also available. Needless to say, it is also possible to apply this method to legal matters.

In addition, as an example of the means for removing residual toner after transfer, we have described a method using a conductive or resistive plan, but the same can be achieved by using a conductive or resistive roller, sponge, rubber, cloth-like member, etc. The effect of this can be obtained.

[Effects of the Invention] As described above, according to the present invention, the accumulated toner can be appropriately discharged, toner can be prevented from falling from the transfer residual toner non-bumping means, and the life of the apparatus can be extended.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram showing a recording apparatus according to an embodiment of the present invention, FIG. 2 is a diagram showing an example of the configuration of a brush, and FIGS. 3 and 4 are diagrams showing experimental results. 1... Photosensitive drum (image carrier) 2...
...Transfer residual toner non-banging means 3...
...Laser device (image exposure means) 4...
...Development cleaning device (development cleaning means) 5...
...Transfer roller (transfer means) 10...Development roller (elastic development member) T...Toner (
developer)

Claims (1)

[Claims] (1) An electrostatic latent image forming means for forming an electrostatic latent image on an image carrier; and a developer charged to the same polarity as the electrostatic latent image is supplied to the image carrier while performing reversal development. A developer cleaning device for removing residual developer; a transfer device for transferring the developer image formed on the image carrier to a transfer target member; and a transfer device for removing residual developer remaining on the image carrier after transfer. In an image forming apparatus having a non-patterning means that slides into contact with a developer and non-patterns an image formed by the residual developer after transfer, an ejection mode is provided in which the developer accumulated in the non-patterning means is redeposited onto the image carrier. Set. An image forming apparatus comprising: applying means for applying an AC bias to the non-patterned member when the ejection mode is set by the setting means.