JPH04141678A - Electrifying and cleaning device - Google Patents

Abstract

PURPOSE:To minizturize a device by moving an image forming body and a rotating roller in opposite directions, applying an AC bias voltage having a DC component to the rotating roller, electrifying the image forming body and eliminating toner stuck on the image forming body. CONSTITUTION:A rotating roller 21 consisting of an elastic body 23 is pressed to an image forming body 1, and the image forming body 1 and the rotating roller 21 are moved in opposite directions on this pressing face 21a. The AC bias voltage having a DC component is applied to the rotating roller 21 to not only electrify the image forming body 1 but also remove toner stuck on the image forming body 1. Consequently, the degradation of the photosensitive body 1 is prevented because ozone is not generated, and electrification and cleaning are simultaneously performed. Thus, the device is miniaturized.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention combines charging of an image forming body of an image forming apparatus such as an electrophotographic copying machine and cleaning to supplement and clean residual toner on the surface of the image forming body. This invention relates to charging and cleaning devices.

[Conventional technology]

Conventionally, a corona charger has generally been used to charge an image forming body of an image forming apparatus. This corona charger is several KV
A high voltage is applied to the discharge wire to generate a strong electric field around the discharge wire to generate a gas discharge, and the image forming body is charged by adsorbing the electrons and charged ions generated at this time.

The corona charger used in such conventional image forming apparatuses can charge the image forming object without mechanically contacting it, so it has the advantage of not damaging the image forming object during charging. are doing. However, since this corona charger uses high voltage, there is a risk of electric shock or leakage, and the ozone generated by gas discharge is harmful to the human body, shortening the life of the image forming body. It had In addition, the charging potential by a corona charger is unstable as it is strongly affected by temperature and humidity.
Furthermore, a corona charger requires a high voltage to obtain a charging potential, which is a major drawback when an electrophotographic image forming apparatus is used as a communication terminal or an information processing apparatus.

Many of the drawbacks of such corona chargers are due to the fact that charging involves gas discharge.

Therefore, a conductive rotating roller is used as a charging device that can charge an image forming body without using a high-pressure gas discharge like a corona charger and without mechanically damaging the image forming body. A charging device for charging an image forming body by injecting charge into the surface thereof was disclosed in Japanese Patent Laid-Open No. 56-10
No. 4346, JP-A-5849960, JP-A-63-1
It is disclosed in publications such as No. 49668.

[Problem to be solved by the invention]

However, even in the charging devices disclosed in the above-mentioned publications such as JP-A-56-104346, JP-A-58-49960, and JP-A-63-149668, the image forming apparatus is There was a problem in that it could not be made smaller.

The present invention solves these problems and eliminates the generation of ozone.
In addition to being able to perform extremely stable and uniform charging,
It is an object of the present invention to provide a charging and cleaning device that also cleans an image forming body and can downsize an image forming apparatus.

[Means to solve the problem]

The above object is to press a rotating roller made of an elastic material against the image forming body, to make the moving direction of the image forming body and the moving direction of the rotating roller opposite to each other on the pressing surface, and to apply the toner to the rotating roller in a direction opposite to that of the rotating roller. This is achieved by a charging and cleaning device characterized in that it applies an AC bias voltage having a polar DC component to charge the image forming body and to remove toner adhering to the image forming body.

〔Example〕

FIG. 1 is a sectional view showing an example of an image forming apparatus to which the present invention is applied. In the figure, ■ is a photosensitive drum which is an image forming member, and is rotating at a linear speed of 150 mm/see in the direction of the arrow.

As shown in FIG. 4, the photosensitive drum 1 is an image forming body having a high γ photosensitive property and is composed of a photosensitive layer IA, an intermediate layer IB, and a conductive support LC. The thickness of the photosensitive layer IA is 5 to 100
It is about μm, preferably 10 to 50 μm. The photoreceptor drum 1 is a drum-shaped conductive support 1C made of conductive metal.
A 0.1 μm-thick intermediate layer IB made of ethylene-vinyl acetate copolymer is formed on the support IC, and a 35 μm-thick photosensitive layer IA is provided on this intermediate layer IB. .

As the conductive support IC, a drum made of aluminum, steel, copper, etc. is used, but there are also belt-shaped ones made by laminating or vapor-depositing a metal layer on a paper-plastic film, or a nickel belt made by electroforming. A metal belt such as the following may also be used. In addition, the intermediate layer IB can withstand a high voltage of ±500 to 2,000 V as a photoreceptor, and for example, in the case of positive charging, it can withstand a conductive support l for electrons.
In order to prevent injection from C and obtain excellent light attenuation characteristics due to the avalanche phenomenon, it is desirable that the intermediate layer IB has hole mobility. It is preferable to add 10% by weight or less of the positively charged charge transporting substance described in the specification.

As the intermediate layer IB, the following resins, which are usually used in photosensitive layers for electrophotography, can be used.

(1) Vinyl polymers such as polyvinyl alcohol (Poval) (2) Nitrogen-containing vinyl polymers such as polyvinylamine (3)
Polyether polymers such as polyethylene oxide (4) Acrylic acid polymers such as polyacrylic acid and its salts (5) Methacrylic acid polymers such as polymethacrylic acid and its salts (6) Ether cellulose such as methyl cellulose (7) Polyethyleneimine-based polymers such as polyethyleneimine (8) Polyamino acids such as polyalanine, (9) Starch and its derivatives such as starch acetate and amine starch, (10) Polyamide such as soluble nylon, etc. The polymer photosensitive layer IA, which is soluble in a mixed solvent of water and alcohol, basically consists of 7 talocyanine fine particles with a diameter of 0.1 to 1 μm, which are made of a photoconductive pigment, and an antioxidant, without using a charge transport substance. is mixed and dispersed in a binder resin solvent to prepare a coating liquid, and this coating liquid is applied onto the intermediate layer IB, dried, and optionally heat-treated to form the intermediate layer IB.

In addition, when a photoconductive material and a charge transport substance are used together, a small amount of the photoconductive pigment and the photoconductive pigment is 115 or less, preferably l/1,000 to l/10 (weight ratio). A photoconductive material comprising a charge transport substance and an antioxidant are dispersed in a binder resin to constitute the photosensitive layer IA.

In an image forming apparatus that forms a color image by superimposing color toner images on a photoreceptor drum l, a photosensitive drum having spectral sensitivity on the long wavelength side is used to prevent the beam from the scanning optical system from being blocked by the color toner image. I need a body;
The toner used is, for example, one having an infrared transmittance with a light wavelength of 750 nm or more as described in Japanese Patent Application No. 1992-92660.

The light attenuation characteristics of the high γ photoreceptor of this example will be explained below. FIG. 3 is a graph showing the characteristics of a high γ photoreceptor.

In the figure, vl is the charged potential (V), Vo is the initial potential before exposure (V), Ll is the amount of laser beam irradiation required for the initial potential v0 to attenuate to 415 (μJ/cm"),
L2 is the initial potential ■. It represents the amount of laser beam irradiation (μJ/cm") required for attenuation to 115.

The preferred range of Lm/L is 1.0≦Lz/Lr≦1.5.

This example Teha VI = 1,0OOV, V, = 950
V, L2/L+ = 1.2. Further, the potential of the photoreceptor at the exposed portion is IOV.

The light attenuation curve is at the initial potential V. Let E be the photosensitivity at a position corresponding to the middle stage of exposure when the voltage is attenuated to 1/2, and let E be the photosensitivity at a position corresponding to the early stage of exposure when the initial potential v0 is attenuated to 971O. . When closed, (E1/□
) / (E 1/1.) ≧ 2, preferably (E 1/2) / (E sz+o) ≧ 5, a photoconductive semiconductor is selected. Here, photosensitivity is defined as the absolute value of the amount of potential drop with respect to a small amount of light.

In the light attenuation curve of this photoreceptor, as shown in FIG. 3, the absolute value of the differential coefficient of the potential characteristic, which is photosensitivity, is small when the amount of light is small, and as the amount of light increases, it becomes a dog and sharply attenuates. Specifically, as shown in Fig. 3, the light attenuation curve exhibits poor sensitivity characteristics and almost flat light attenuation characteristics during a short period L1 at the beginning of exposure, but from mid-exposure period L1 to L2. , and becomes ultra-high sensitivity, resulting in an ultra-high γ characteristic that decreases almost linearly. Specifically, this photoreceptor is +500~+
It is thought that high γ characteristics are obtained by utilizing the avalanche phenomenon under high charging of 2,000 VQ. In other words, carriers generated on the surface of the photoconductive pigment in the early stage of exposure are effectively trapped in the interface layer between the pigment and the coating resin, and light attenuation is reliably suppressed, resulting in an extremely rapid avalanche in the middle stage of exposure. It is understood that a phenomenon occurs.

At the top of the main body of the image forming apparatus, a document table 31 made of a transparent glass plate or the like, and a document cover 32 that covers the document placed on the document table 31 are arranged.

A first mirror unit 5 including an exposure lamp 11 and a first mirror 12 is located below the document table 31 and inside the apparatus main body.
is installed parallel to the document tray 31 and movable in a straight line in the horizontal direction in the drawing, and optically scans the entire surface of the document tray. 13 and 14 are a second mirror and a third mirror, respectively, and the second mirror unit 6 in which these mirrors are integrated is moved in the same left and right direction at a speed 172 of the first mirror unit 5 so as to maintain a predetermined optical path length. move in a straight line. Of course, the movement of the second mirror unit 6 is parallel to the document table 31 similarly to the first mirror unit 5. An image of the document on the document table 31 illuminated by the exposure lamp 11 is formed on the CCD 16 by the main lens 15 via the first mirror 12 , the second mirror 13 , and then the third mirror 14 . After image processing the input image, the laser optical system 17
The photoreceptor drum 1 is scanned with light. When scanning is completed, the first mirror unit 5 and the second mirror unit 6 return to their original positions and wait until the next copy.

The photosensitive drum 1 rotates clockwise as indicated by the arrow at the same time as copying starts, and is charged by a charging and cleaning device 2, which will be described in detail later. An electrostatic latent image corresponding to the image of the document is formed thereon. After that, the photoreceptor drum
The upper electrostatic latent image is reversely developed by the developing device 3 and becomes a visible toner image. That is, a magnet roll of the developing device 3 is built in; a DC or even AC bias voltage is applied to the developing sleeve 31, and non-contact development is performed using a two-component developer serving as a developing means to form a toner image. be done.

Non-contact development using a two-component developer is a preferred developing means when a color image is formed by superimposing color toner images on the photoreceptor drum 1, but when forming a monochrome image, non-contact development using a two-component developer is preferred. A contact developing device or a developing device using an l-component developer may be used. Furthermore, by using a developing bias having an alternating current component, it is possible to efficiently develop an electrostatic latent image formed by a high γ photoreceptor.

From a paper feed cassette 4 that accommodates a large number of recording papers P, the recording papers P are fed out one by one by a first paper feeding roller 41 . This fed-out recording paper P is fed onto the photosensitive drum 1 by a second paper feed roller 42 that operates in synchronization with the toner image on the photosensitive drum 1.

The toner image on the photosensitive drum 1 is transferred to the recording paper P by the action of the transfer roller 7, and the toner image on the photosensitive drum 1 is transferred to the recording paper P.
After being separated from the top, it is sent to the fixing device 9 via the recording paper transport means 8, where it is fused and fixed by a heat fixing roller and a pressure roller, and then ejected to a tray 35 outside the apparatus by a paper ejection roller 43.

On the other hand, the toner remaining without being transferred onto the surface of the photosensitive drum 1 is neutralized by the pre-cleaning exposure device 18, and then collected and cleaned by the charging and cleaning device R2, and is ready for the next copying.

FIG. 2 is an enlarged sectional view showing an embodiment of the present invention used in the image forming apparatus shown in FIG. In the figure, 21 is a rotating roller, 25 is a blade, 26 is a bias power source for applying a bias voltage to the rotating roller 21, 28 is a casing, 29 is a recovery screw 21a, and a photosensitive drum l is connected to the rotating roller 21. The nip portion of the press-contact portion, T, is toner.

The rotating roller 21 has a volume resistivity of 10'Ω·cm to 10”Ω around a metal shaft 22 made of stainless steel, for example.
・For example, NBR with an outer diameter of 30 mm adjusted to less than cm
A sponge-like elastic body 23 made of rubber or the like is provided. Further, the surface of the elastic body 23 has a thickness of 10 to 100 μm, for example.
m thickness and volume resistivity of 10"Ω・C10 or more, preferably 1
A high-resistance layer with a resistance of less than 0"Ω・Cm, the surface of which is the diameter of the toner (
It may be covered with a high-resistance film 24 having roughness approximately equal to 20 μm).

Both ends of the metal shaft 220 are bearings, which support the spring 2.
7, the rotating roller 21 is pressed by the photoreceptor drum l.
are pressed against each other to form a nip portion 21a with a nip radius of 2 to 3 mm.

Note that the elastic body 23 or the high-resistance film 24 of the rotating roller 21
It is desirable that the triboelectric charging system between the toner and the toner T improves cleaning performance by triboelectrically charging the toner and the toner.

Furthermore, a material is selected that does not change the polarity of the charge that the toner T originally has.

The bias power supply 26 is a power supply using, for example, an iron resonant transformer, whose primary side is connected to a commercial power supply, and whose secondary side is supplied with toner T, which varies depending on the charging potential of the photoreceptor drum 1 and other conditions, but in the case of reversal development. The charging polarity is equal to or slightly lower than the charging voltage of the photoreceptor l of the same polarity, 600 to 1,0
The DC component of OOV has a frequency of 300 to IOK Hz,
It outputs an AC bias voltage with a peak-peakt voltage of 200 to 3,500 V, preferably 500 to 1,000 V, on which an AC component is superimposed.

This AC bias voltage is applied to the rotating roller 21 via the protective resistor 26a and the metal shaft 22.

If the voltage of the alternating current component is lower than the above range, cleaning will be insufficient, while if it is too high, the photosensitive layer 1A and intermediate layer IB of the photosensitive drum 1 will be destroyed. Note that the bias power supply 26 performs constant voltage control for the DCm component and constant current control for the AC component.

In addition, in the above embodiment, FIG. 5 shows the results of changing the frequency and voltage of the AC voltage component applied to the rotary roller 21.

In Figure 5, the shaded area with vertical lines is the area where dielectric breakdown is likely to occur, the shaded area with diagonal lines is the area where uneven charging is likely to occur, and the unshaded area is stably charged. This is a preferable range in which .

As is clear from the figure, the preferred range changes somewhat with changes in the AC voltage component. Note that the waveform of the AC voltage component is not limited to a sine wave, but may be a rectangular wave or a triangular wave. Furthermore, in FIG. 5, the low frequency region shaded with scattered dots is a range where charging unevenness occurs due to the low frequency.

Next, the operation of this charging and cleaning device 2 will be explained.

The photoreceptor drum l, which has transferred the toner image onto the recording paper P, continues to rotate and reaches the pre-cleaning exposure device 18, where the photoreceptor drum 1 is once photostatically neutralized and then charged to the same polarity as the photoreceptor drum l. . As the photoreceptor drum 1 moves, this toner T approaches the rotation roller 21 rotating in the opposite direction, and when the toner T moves in the opposite direction to the photoreceptor 1, it moves at the same speed as the photoreceptor.
The AC component of the AC bias voltage applied to the rotary roller 21, which rotates at ~2.0 times the circumferential speed, vibrates and easily separates from the surface of the photoreceptor drum 1. It is peeled off, attached to a sponge-like elastic body 23 or a high-resistance film 24 having an uneven surface, and transported. The toner T conveyed by the rotating roller 21 is
It is scraped off toward the bottom of the casing 28 by the blade 25. The scraped off toner T is transported by a transport screw 29 to a toner collection box (not shown) or to the developing device 3 and collected as recycled toner.

Further, on the downstream side of the nip portion 21a, charge is injected from the rotating roller 21 into the photosensitive layer IA of the photosensitive drum l, and the DC component of the AC bias voltage applied to the rotating roller 21 or slightly lower than the charged to a potential.

The case where the bias voltage applied to the rotating roller 21 of the charging and cleaning device 2 configured as described above is made to have only a DC component, and the case where the case where an AC bias voltage having a DC component as described above is used are alternately applied over a long period of time. As a result of comparison, when using AC bias voltage, compared to when using only DC component,
It was observed that the toner recovery rate was improved by about 15%.

It was also confirmed that by using an AC bias voltage, extremely stable charging could be achieved.

In this embodiment, non-charging can be achieved by setting the DC component of the AC bias voltage to zero.

Alternatively, this can be done by retracting the charging and cleaning device 2 from the photoreceptor drum 1.

Note that even if the recovery of the toner T by the rotating roller 21 is incomplete, in the case of reverse development as in this embodiment, the toner T is charged to the same polarity as the photoreceptor, so that no non-image is collected during development. The toner adhering to the area is collected by the developing device and does not adversely affect the image quality.

On the other hand, regular development is performed, and toner T is applied to the positively charged photoreceptor.
When the toner T is negatively charged, the toner T is negatively charged by the charging and cleaning device 2 following the pre-cleaning exposure device 18 provided upstream of the main charging and cleaning device 2, so that the toner T is positively charged. It is efficiently collected by the rotating roller 21 to which a bias is applied, making it an excellent charging and cleaning device.

Further, in an image forming method in which a photoreceptor drum l having a high γ characteristic is imagewise exposed to infrared light such as a semiconductor laser, and reversal development is performed as in the embodiment shown in FIG. When toner T is used, even if a small amount of toner T remains on the photoreceptor 1, it does not pose a problem in forming a latent image as long as it does not accumulate in one area. Therefore, in this embodiment, the toner T was collected in a sufficiently satisfactory state by the rotary roller 2;
Since it has a leveling effect of dispersing it evenly on the top, no problem occurs.

〔Effect of the invention〕

According to the present invention, with the configuration described above, by applying an AC bias voltage having a DC component with a polarity opposite to that of the toner charge to the rotating roller, the recovery rate of residual toner is high and ozone generation is suppressed. Since there is no charger, deterioration of the photoreceptor can be prevented, and since charging and cleaning can be performed at the same time, it is possible to provide an excellent charging and cleaning device that can downsize the image forming apparatus.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an example of an image forming apparatus to which the present invention is applied, FIG. 2 is an enlarged sectional view showing an embodiment of the present invention, and FIG. 3 is a graph showing the light attenuation characteristics of a high γ photoreceptor. , FIG. 4 is a sectional view showing the structure of the high-gamma photoreceptor, and FIG. 5 is a charging characteristic diagram when the frequency and voltage of the AC voltage component are changed. 1... Photosensitive drum 2... Cleaning device 18... Pre-cleaning exposure unit 21... Rotating roller 22... Metal shaft 23.
...Elastic body 24...High resistance film 25...
・Blade 26...Bias power supply 27・
・Spring 29 ・Recovery screw number (KHz)

Claims (2)

[Claims] (1) A rotating roller made of an elastic body is brought into pressure contact with the image forming body, and on the pressing surface, the moving direction of the image forming body and the moving direction of the rotating roller are opposite directions, and the rotating roller has a DC component. A charging and cleaning device characterized by applying an AC bias voltage to charge the image forming body and to remove toner adhering to the image forming body. (2) The charging and cleaning device according to claim 1, wherein the DC component has a polarity opposite to that of the toner.