JP2667560B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention forms a residual latent image on an image carrier such as a photoconductor,
The present invention relates to an image forming apparatus that develops this electrostatic latent image and records it on a transfer material such as paper.

(Prior Art) As this type of image forming apparatus, an electrophotographic apparatus, an electrostatic printer, and the like are known. In these image forming apparatuses, after an electrostatic latent image is formed on a photoconductor, a developer is electrostatically attached to the electrostatic latent image to form a developer image, and then the developer is formed on paper. The transcript is used for recording. Further, since the electrostatic latent image and the developer that cannot be transferred remain on the photoreceptor after the transfer, the residual developer is removed by a cleaning device, and then the electrostatic latent image is removed by a charge removing device. doing.

By the way, in recent years, downsizing of an apparatus has been required. For example, Japanese Patent Application Laid-Open No. 47-11538 discloses a method of downsizing the apparatus by using a single apparatus as a developing apparatus and a cleaning apparatus. ing. This method is generally called a two-cycle method. In one developing device, the electrostatic latent image is developed when the photosensitive drum passes here in the first rotation, and then the developing device is passed in the second rotation. To remove the residual image after the transfer.

However, in the conventional method, the residual image must be removed from the developing device when the photosensitive drum approaches the second pass, so that the recording speed is reduced by half and the peripheral speed of the photosensitive drum is reduced. There is a problem that a recording size larger than the size of the entire surface cannot be obtained, and the photosensitive drum must necessarily be larger than the required recording paper size, which is an obstacle to miniaturizing the device. I was

On the other hand, US Pat. No. 364926 uses a developing device that simultaneously develops the electrostatic latent image and cleans the developer remaining after the previous transfer when the electrostatic latent image first passes. Thus, a method is disclosed for overcoming the drawbacks relating to speed.

(Problems to be Solved by the Invention) However, in this conventional apparatus, the subsequent charging, electrostatic latent image formation, and development are performed from above while leaving the residual image after transfer on the photosensitive drum. Will be. Therefore, in the charging, the remaining latent image and the toner image are superimposed and charged, and further uniform exposure and the formation of the latent image are impaired in order to perform the next image exposure from above the toner image, The afterimage of the previous process appears as a so-called memory image (ghost image) overlapping on the next screen, and has a disadvantage that the fidelity of the image is impaired. Such development is particularly likely to occur when a solid portion (a region where the developer is attached to the entire surface over a wide range) and a residual image such as a character formed in the previous step are encountered. Moreover, since the residual developer cannot be removed sufficiently, the developer image also remains as a cleaning memory (afterimage memory) and is often directly transferred to the sheet to present a contaminated image.

For this reason, the present inventor has already disclosed in Japanese Patent Laid-Open No. 63-242587 a device for mechanically and electrically unpatterning (deleting an afterimage) a developer image remaining after transfer onto an image carrier by a disturbing means. Has been proposed.

However, even in such an image forming apparatus,
Naturally, it is required to further improve the non-patterning function and further improve the image quality.

The present invention has been made in consideration of such a conventional situation, and an object of the present invention is to provide a small-sized, high-quality image forming apparatus that reliably prevents generation of a history image.

[Structure of the Invention] (Means for Solving the Problems) In order to solve the above problems, the present invention provides a charging unit for charging a photoconductor provided along a predetermined direction to a specific polarity, and the charging unit. And an elastic developing roller carrying a one-component developer charged to have the same polarity as the specific polarity, and an elastic developing roller for exposing the charged photosensitive member to form an electrostatic latent image. By pressing the roller against the photoconductor and slidingly contacting it, the developer on the elastic developing roller is supplied to the electrostatic latent image formed by the exposing means to perform reverse development, and at the same time, A developing and cleaning unit for removing a residual developer on the photoconductor; and a transfer medium provided on the photoconductor on which a developer image is formed by the developing and cleaning unit. An agent image is transferred from the photoreceptor to the transfer material A transfer roller for copying, a first voltage application unit for applying a transfer voltage for transferring the developer image to the transfer roller, and the photoconductor is disposed facing the photoconductor along the predetermined direction. Having a plurality of contact members provided in contact with the photoconductor so as to form irregularities between the photoconductor,
Disturbing means for disturbing the residual developer remaining on the photoreceptor after transfer is performed by the transfer roller with the contact member; and a DC voltage for disturbing the residual developer by the disturbing means. A second voltage applying means for applying a deviated AC voltage, wherein the plurality of contact members are a first end slidably provided on the photoconductor and a second end different from the first end. An orientation angle in which a plurality of line segments connecting the first end portion and the second end portion have a uniform orientation angle with respect to the side edge of the disturbing member that has respective end portions and is substantially orthogonal to the predetermined direction. Are arranged so as to have

(Operation) In the image forming apparatus of the present invention having the above-described structure, the developer having the same polarity as that of the image carrier is used for reversal development to weaken the adhesive force of the developer to the image carrier and clean the residual developer. To facilitate.

Further, as the disturbing means, a film-shaped member that elastically presses the image carrier, or a member having an uneven shape in which the rubbing surface has directionality by elastically pressing the image carrier (for example, the uneven shape is Having a film-like member, a brush-like member having conductive fibers implanted diagonally)
A wide contact width can be obtained with a light pressure.

As a result, the disturbing means surely comes into contact with the residual developer image, so that the residual image is more reliably disturbed by mechanical contact, and at the same time, the residual developer is temporarily absorbed and captured electrically, but is discharged again. Thus, the cleaning operation can be performed more reliably, and the developer can be returned to the image carrier again without being stored unilaterally, and can be reliably cleaned by the same device (developing cleaning device) at the same time as the development.

For this reason, the size of the image carrier such as the photoconductor can be made smaller than the size of the required image, and the dedicated collected developer accommodating section (cleaning device) can be eliminated.

As a result, it is possible to provide a small, high-quality image forming apparatus that reliably prevents generation of a history image.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows an image forming apparatus according to the present embodiment. As an image carrier having a recording surface smaller than the area of an image to be recorded (that is, a small diameter) in a substantially central portion of a main body H thereof. Photosensitive drum 1 is disposed. The photoreceptor drum 1 is made of an organic photoreceptor (OPC) type photoconductive material or the like, and has a predetermined speed (80 mm /
Seconds).

Further, around the photosensitive drum 1, along the rotation direction thereof, a charging charger 2, a laser device 3, a developing / cleaning device 4, a transfer roller 5, a charge eliminating lamp 6, and a disturber 7 are arranged in this order. ing.

The charging charger 2 is located above the photosensitive drum 1, and the surface of the photosensitive drum 1 is -400 to -100.
It is designed to be negatively charged substantially uniformly at 0V.

Further, the laser device 3 irradiates the surface of the photosensitive drum 1 with a laser beam 8 in accordance with image information to be recorded, and forms an electrostatic latent image on a charged area.

Further, the developing cleaning device 4 is provided with a hopper 9 for accommodating a so-called one-component developer T (volume average particle diameter of 6 to 15 μm) having triboelectricity. In the hopper 9, there is provided a developing roller 10 that conveys the developer T toward a position facing the photoconductor drum 1 and returns the developer T remaining on the photoconductor drum 1 into the hopper 9. ing. The developing roller 10 is provided with a conductive surface layer 11 having an electric resistance of 10 ² to 10 ⁸ Ωcm, and an elastic layer 12 made of urethane foam, silicone rubber, diene rubber (EPDM), or the like arranged inside the conductive surface layer 11. As an elastic roller. An elastic blade 13 made of phosphor bronze, urethane or silicone resin for forming a thin layer is pressed against the developing roller 10 while frictionally charging the developer T, and the developer T passing therethrough is exposed to light. One to three developer layers (6 to 3) having negative triboelectric charge of the same polarity as the body drum 1
45 μm thick). The surface of the developing roller 10 needs to be selected in consideration of frictional charging with the developer T or appropriate elasticity and friction. As the material of the surface layer 11, for example, 10 to 30 conductive carbon in urethane resin is used.
It is formed by applying a mixture of weight%. further,
A bias power source 14 is connected to the developing roller 10 and is electrically connected to the surface layer 11. As a result, a predetermined developing bias is applied during development and cleaning. A sponge-like developer transport roller 15 is further provided in the hopper 9, and plays a role of preventing the developer T in the hopper 9 from aggregating and transporting and supplying.

Further, the transfer roller 5 is provided substantially below the photosensitive drum 1 and facing the peripheral surface of the photosensitive drum 1 via a paper conveyance path 16. The transfer roller 5 has the same structure as that of the developing roller 10, but the electric resistance of the surface layer is 10 ⁵ to 10 ¹⁰ Ωcm. This transfer roller 5
Due to this, 800-220 on the back side of the paper 17 conveyed here
The toner image is transferred from the photosensitive drum 1 to the paper 17 by applying a voltage of 0 V to electrostatically attract the toner. With such a contact type transfer means, stable transfer characteristics are exhibited even under high humidity, so that the amount of residual transfer developer can be reduced and the cleaning load can be reduced. Removed to prevent mixing into the developer.

The disturber 7 is constructed as shown in FIGS. 2 and 3. That is, the disrupter 7 is 10 ³ to 10 ⁹
Ωcm, preferably 10 ⁵ ~ 10 ⁸ Ωcm conductivity, thickness 20
A film-like rubbing member 7a having an elastic force of about 1000 μm and a width of about 10 to 50 mm, and a pressing member 7b made of urethane foam, felt or the like provided to press the rubbing member 7a from behind, It is composed of a pair of support members 7c and 7d made of a conductor such as aluminum or iron, which sandwiches the rubbing member 7a and presses and supports the pressing member 7b. The disrupter 7 is a housing of a process unit main body in which the photosensitive drum 1 or the developing cleaning device 4 is integrated.
A portion of the photosensitive drum 1 is fixed to a part of the photosensitive drum 1 by a screw or the like so that the abdominal surface is pressed against the photosensitive drum 1 in the longitudinal direction.
The rubbing member 7a is connected to a power supply 19 so that a predetermined voltage is applied.

Note that FIG. 2 shows a cross section of the disturber 7, and the actual disturber 7 is designed to slide over the entire area of the photosensitive member 1 in the longitudinal direction as shown in FIG.

The rubbing member 7a is rubbed with the contact width (nip) of about 2 to 10 mm as the photosensitive drum 1 rotates, and a voltage of 0 to 700 V, preferably 400 to 600 V is supplied by the power supply 19. I have. Here, the rubbing member
7a has an appropriate elasticity as described above, and the rubbing surface is a rough surface having an appropriate unevenness of about 1/5 to 2 times (2 to 20 μm) the toner particle size. However, the transfer residual developer on the photosensitive drum 1 exerts an appropriate frictional force. There is no friction to scrape off the toner. Furthermore, by doing so, the residual toner is surely contacted, and the residual image is surely disturbed to make it unreadable, that is, unpatterned, and the residual electrostatic latent image is also made conductive. The charge is removed by the rubbing member 7a and erased.

Here, the negative polarity developer is further attracted to the rubbing member 7a by the positive polarity bias voltage, and the residual image on the photosensitive drum 1 is electrically peeled and cleaned. However, at the next moment, the developer nipped between the photoreceptor drum 1 and the rubbing member 7a,
If a high voltage is applied to this gap of only 30 to 60 μm, a polarity reversal phenomenon of the developer, which is considered to be caused by charge injection or discharge to the developer, can occur, and the developer is attracted to the rubbing member 7a. It is possible to eject the collected developer again to the image carrier side.

For this reason, the developer is not unilaterally captured and accumulated on the rubbing member 7a, and the residual developer is always captured and discharged in a constant cycle, which disturbs the residual image and makes it unreadable. Only the non-patterning function acts to prevent the developer from excessively accumulating and falling or scattering.

Prior to these, since the negative charging of the photosensitive drum 1 has been erased by the erasing lamp 6, the rubbing member 7a
Has an effect of mainly eliminating the positive side charge.

The material of the rubbing member 7a is a film made by mixing and dispersing 5 to 20% by weight of conductive carbon or metal fiber (filler) in polyester, polyurethane or fluororesin. This contributes to a reduction in the driving torque of the photosensitive drum 1 and is easy to use.

A paper supply unit 20 that supplies the paper 17 to the transport path 16 is provided below the photosensitive drum 1. The paper feeding unit 20 accommodates a paper 17 to which an image is transferred. Above the paper supply unit 20, a paper supply roller 21 that supplies paper 17 from the paper supply unit 20 to the transport path 16 by rotation.
Is provided. Note that the transport path 16 is provided with a fixing device 22 for fixing the developer image after transfer to the paper 17.

Next, the operation of the electronic copying apparatus according to the present embodiment will be described.

The photosensitive drum 1 is rotated at a predetermined speed in the direction of arrow A, and the surface of the photosensitive drum 1 is corona-charged to about -400 to -800 V by the charging charger 2.

Subsequently, the charged area is irradiated with a laser beam 8 from the laser device 3 to form an electrostatic latent image on the surface of the photoconductor 1.

The electrostatic latent image is then conveyed to the developing and cleaning position facing the developing and cleaning device 4. Developing roller 10 of developing cleaning device 4
Sends a developer (hereinafter, referred to as a toner) T,
This comes into contact with the electrostatic latent image elastically and with a nip width due to deformation, causing the toner T to adhere to form a toner image. In this case, the toner T adheres to the light irradiation area and is subjected to so-called reversal development. Toner T having an average particle size of 8 to 15 μm is used, and the surface layer of blade 13 and developing roller 10 is
It is charged to about -5 to -30 μc / g (microcoulombs / gram) by friction with 11, and a voltage of about -150 to -450 V is applied to the developing roller 10.

The toner image after development is conveyed to a transfer area facing the next transfer roller 5. On the other hand, the paper feed roller
With the rotation of 21, the paper 17 is sent from the paper feeding unit 20 in synchronization with the rotation of the photosensitive drum 1. The back surface of the paper 17 is charged to a positive polarity by the transfer roller 5.
Therefore, the toner image on the surface of the photosensitive drum 1 is electrostatically attracted to the paper 17 and transferred. Here, the transfer roller 5 is supplied with a voltage of 1000 to 2000 V from its DC power source 23 on its rotating shaft, and is made by mixing 30 to 40% by weight of conductive carbon with silicon resin provided at both ends of the transfer roller 5. A voltage is applied to the conductive surface portion of the roller surface of 10 ⁵ to 10 ⁹ Ωcm through the portion. It should be noted that the surface of the transfer roller 5 is preferably made of a material having surface smoothness and low friction in order to facilitate cleaning of foreign matters such as developer and paper dust that adhere to it. In this example, conductive polyfluoride is used. A resin, a conductive polyester, or the like is used, and can be satisfactorily cleaned by the cleaning blade 24. The transfer roller 5 having a flexible rubber hardness of 25 to 50 ° in comparison with the JIS method in terms of the rubber hardness of the entire transfer roller had a good tolerance for the pressing force of the transfer roller 5 against the photosensitive drum 1.

The sheet 17 after the transfer is sent to the fixing device 21, where the toner is melted and fixed on the sheet 17, and then discharged.

On the other hand, on the surface of the photosensitive drum 1 after the transfer, a small amount of the toner image that remains without being transferred or the positive and negative electrostatic latent images that remain after the toner transfer remains.
These toner images or electrostatic latent images are first erased by an erase lamp 6 to remove a negative latent image, and then conveyed to a disruptor 7 where they are disturbed and non-patterned.

In the disturbing device 7, the rubbing member 7a is brought into contact with the electrostatic latent image to exert a mechanical and electrostatic force so that the toner image and the electrostatic latent image that remain are finely divided into an unreadable or unreadable state. Disturb the image. In this case, since the toner T remaining on the photosensitive drum 1 has a polarity opposite to that of the voltage initially applied to the rubbing member 7a as described above, it is electrostatically attracted to the rubbing member 7a. . However, after several tens of seconds to several seconds, the polarity becomes the same by the mechanism described above, and the photosensitive drum 1
Are discharged one after another. This discharge characteristic is the same as the toner T
Since it is affected by the electric resistance and the amount of electric charge, or the magnitude of the applied voltage and the electric resistance of the rubbing member, the contact width, the pressing force, etc., it is necessary to experimentally optimize these elements. In any case, what is dominant is the magnitude of the applied voltage, at least the magnitude at which charge injection occurs in the toner T (approximately
400V or more) is required. That is, if this voltage is too low, the toner T will unilaterally accumulate on the rubbing member 7a, and if it is too high, the disturbing effect will be reduced and the photosensitive drum 1 will be destroyed.

The greatest purpose of optimizing various parameters in this way is to prevent the toner T from being accumulated in the rubbing member 7a. The residual image is disturbed, and most of the toner T is scattered in the form of a mist on the surface of the photosensitive drum 1 and adheres thereto, but hardly accumulates in the disturber 7. That is, the disrupter 7 does not have a function as a cleaning device, but has only an auxiliary function of the developing cleaning device 4. The toner T scattered on the surface of the photosensitive drum 1 in this manner is distributed in a sufficiently small mist state, and no longer has information as characters or images.

Next, the disturbed area is further rotated and conveyed again to a position facing the charging charger 2, and is corona-charged over the scattered toner T. After the charging, the latent image is exposed by the laser device 3 to form an electrostatic latent image, and reaches the developing cleaning position facing the (second) developing cleaning device 4 again. In this case, in the electrostatic latent image formed for the second time, an exposed portion (an image portion to which toner is to be attached)
Also, in the non-exposed area (non-image area), the residual toner T is greatly reduced by the roller transfer, and the residual toner T is dispersed almost uniformly and sufficiently thin in advance. No unevenness occurs. Therefore, the second
Even in the second development, the image is kept uniform because the residual potential becomes uniform after exposure. Here, as described above, the developing roller 10 has an elasticity of 30 to 70 ° according to the JIS rubber hardness measurement method, has an electrical conductivity of 10 ² to 10 ⁸ , and has a linear load of 20 to 150 g on the developing roller 10. By applying a load of / cm and pressing and rubbing at a speed difference of 1.05 to 4 times, a contact width (nip) of 1 to 4 mm is generated. In this nip, the residual toner and the toner T on the developing roller 10 are However, since they are rubbed and disturbed, a strong frictional force is generated, and the cleaning ability is enhanced. However, since the developer is formed only with the toner T, there is no occurrence of streak or crest-like image quality deterioration. Further, in the non-exposure portion, the toner T attached to the photosensitive drum 1 because the suction force by the developing bias is superior to that of the photosensitive drum 1 is successively attracted to the developing cleaning device 4 and collected. That is, by applying a developing bias having a value between the residual potential of the exposed portion and the voltage of the non-exposed portion to the developing roller 10, new toner T adheres from the developing roller 10 to the exposed portion, and at the same time, Residual toner adhering to the non-image area is attracted and collected by the developing roller 10 from here. In this case, since the residual toner is small and is dispersed in the form of a small mist in the disrupter 7 in advance, the developing and cleaning device 4 can effectively collect the residual toner.

In this way, the photosensitive drum 1 is rotated and used repeatedly to obtain one recording image. After the development and cleaning, the toner image is transferred to the sheet 17 at a position facing the transfer roller 5. Hereinafter, similar steps are repeated.

According to this embodiment, even if the photoreceptor drum 1 having a small diameter is used, not only the occurrence of a memory image, which has conventionally occurred, is eliminated, but also a cleaning failure can be prevented.

According to this embodiment, when an image having an image area ratio of 7% is printed on 20,000 sheets of A4 size paper, no memory image is generated or cleaning failure occurs, or excess toner is accumulated in the disturber 7. As a result, a good image could be obtained until the end without any trouble such as toner T overflowing from the apparatus.

In the above embodiment, the case where one rubbing member is used has been described, but a plurality of rubbing members may be used. For example, in the case where the photosensitive drum 1 is formed in two columns, positive and negative biases of different polarities are applied to ensure that the residual developer on the photosensitive drum 1 functions even when the positive and negative polarities are mixed. it can.

Further, in the above-described embodiment, the case where the power supply 19 is a DC power supply has been described. However, even when the power supply 19 is set to AC, the same effects can be obtained by providing the following predetermined conditions.

That is, a peak voltage and a frequency (approximately 250V to 1000V, 300Hz to 5KHz, preferably 300 to 700) that are sufficient to electrostatically adsorb the residual toner adhering to the photosensitive drum 1 are obtained.
V, 400 Hz to 3 KHz), and by applying an AC voltage whose polarity changes to positive or negative (that is, alternating), a mode in which the toner T is adsorbed and a mode in which the toner T is ejected (repelling) as in the case of DC Are alternately generated, and the toner T
Can also be arbitrarily controlled.

That is, the polarity of the toner T is 50 to 40
By superimposing a DC bias of 0 V, a biased AC voltage can be applied to change the charge of the toner to the biased polarity side. Actually, it is preferable that the toner is deviated to the original polarity side of the toner, so that the collection by the developing roller 10 can be reliably performed. Such an AC voltage application has a better memory erasing function than the DC application described above, and is more preferable.

In the above embodiment, the case of using the contact type non-magnetic-component developing method has been described, but other methods such as the magnetic-component brush method, the two-component magnetic brush method, the fur brush method and the like may be used. It goes without saying that this is feasible.

Further, the contact side surface of the rubbing member 7a may be a fine grain surface as described above, but as shown in FIG. 4, it is deep in a direction oblique to the rubbing direction (arrow in the figure) with the photoconductor drum 1. 5-50
By using one with a large number of grooves (or projections, irregularities) of about 0 μm and a pitch of about 20 to 600 μm,
Since the function to mechanically shift the position of the residual toner diagonally is added, the memory erasing ability becomes extremely high, but toner is unnecessarily blocked and accumulated, resulting in side effects such as dropping and scattering. There is provided an excellent rubbing member without any. It should be noted that the groove in FIG. 4 is drawn in an exaggerated manner and differs from the actual relative size. Specifically, this groove processing can be realized, for example, by grinding the above-mentioned film material in a certain direction using an abrasive of about 50 to 400. It is also possible to use another processing method using a mold or the like.

Further, as the rubbing member having the uneven shape having such a directionality, in addition to this, as shown in FIG. 5, the conductive fibers 25 are planted obliquely with respect to the rubbing direction and made of metal or the like. The one fixed by the bundling member 26 can be used favorably. When the rubbing member having this shape is used in combination with the above-described method of applying an AC voltage, a very good memory (ghost) image erasing function with little dependence on the type (shape) of the residual image or environmental change is exhibited.

[Effects of the Invention] As described above, according to the present invention, it is possible to provide a small-sized and high-quality image forming apparatus in which generation of a history image is reliably prevented.

[Brief description of the drawings]

1 is a diagram showing the overall configuration of an image forming apparatus according to an embodiment of the present invention, FIGS. 2 and 3 are diagrams showing the configuration of a disturber of the image forming apparatus of FIG. 1, FIG. 4 and FIG. FIG. 5 is a diagram showing a main configuration of a disturber in another embodiment. 1 ... Photosensitive drum (image carrier) 3 ... Laser device (electrostatic latent image forming means) 4 ... Development cleaning device (development cleaning means) 5 ... Transfer roller (contact type transfer means) 7 ... Disturbance Hand device (disturbing means) T: toner (developer) 17: paper (transfer material)

Claims (1)

(57) [Claims] A charging unit configured to charge a photosensitive member provided along a predetermined direction to a specific polarity; and an exposure unit configured to expose the photosensitive member charged by the charging unit to form an electrostatic latent image. Means, comprising an elastic developing roller carrying a one-component developer charged to the same polarity as the specific polarity, by sliding the elastic developing roller against the photoconductor while pressing against the photoconductor,
Developing cleaning means for supplying a developer on the elastic developing roller to the electrostatic latent image formed by the exposing means to perform reversal development and, at the same time, removing residual developer on the photoreceptor; A transfer roller that is provided facing the body surface and presses a transfer material onto a photoconductor on which a developer image is formed by the developing and cleaning unit, and transfers the developer image from the photoconductor to the transfer material. A first voltage application unit that applies a transfer voltage for transferring the developer image to the transfer roller; and a first voltage application unit that faces the photoconductor along the predetermined direction, and is disposed between the photoconductor and the photoconductor. A plurality of contact members provided in contact with the photoreceptor so as to form irregularities on the photoreceptor; Disturbing means for disturbing the agent; A second voltage applying means for applying an alternating voltage biased by a direct current voltage for disturbing the residual developer to the means, wherein the plurality of contact members are slidably provided on the photoconductor. And a second end different from the first end and each of the first end and the second end with respect to a side end of the disturbing member substantially orthogonal to the predetermined direction. An image forming apparatus, wherein a plurality of line segments connecting the sections are arranged so as to have a uniform orientation angle.