JPH05181347A - Electrophotographic charging device - Google Patents

Abstract

PURPOSE:To provide an electrophotographic charging device having less ozone generating quantity with a simple structure. CONSTITUTION:A rotating electrophotographic photoreceptor enclosing magnets 15, 16 the positions of which are fixed so as to never follow the rotation of a photoreceptor drum and an electrode 17 arranged in opposition to a magnet 18 through the clearance with the photoreceptor 14 are provided. A magnetic powder 19 is attracted between the photoreceptor 14 and the electrode 17 by the magnetic force of the magnet 18, and an AC voltage is applied to the electrode 17, whereby the photoreceptor 14 is charged.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic charging device applicable to printers, facsimiles and the like.

[0002]

2. Description of the Related Art Conventionally, various electrophotographic methods have been devised for charging a photoconductor. For example, a typical one is a corona charger. Although the corona charger has a stable charging function and is widely put to practical use, since it generates a large amount of ozone, a charger that does not use corona discharge is being developed in recent years from the viewpoint of environmental preservation in the office. (Journal of the Electrophotographic Society, 27.4, 573 (198
8)). Those using elastic rollers
-267667), a contact charging method using conductive particles (Journal-Applied-Physics 62, 2665).
(1987)).

Among them, the contact charging method using conductive particles will be described in some detail with reference to FIG. In FIG. 3, 1
Is an electrophotographic photosensitive member formed on the conductive substrate 2. 3 is a fixed sleeve, 4 is a rotating magnet roller provided in the sleeve 3, 5 is conductive magnetic powder, and 6 is a high-voltage power supply for applying a voltage to the sleeve 3.

The operation of the electrophotographic charging device configured as described above will be described. When the magnet roller 4 is rotated, the magnetic powder moves to the side opposite to the arrow. When a voltage is applied to the sleeve 4 with a high-voltage power source, electric discharge occurs in a minute space between the magnetic powder and the photoconductor, and the photoconductor is charged.

[0005]

However, in the above structure, the magnetic restraining force of the magnet roller against the magnetic powder is small, and the magnetic powder loses the electrostatic attraction of the photoconductor and adheres to the photosensitive pair side and is carried away. It has been found that this will adversely affect the subsequent exposure and development steps.

In view of the above problems, the present invention provides an electrophotographic charging device having a simple structure and capable of providing stable charging.

[0007]

In order to solve the above problems, the present invention relates to an electrophotographic photosensitive member which contains a magnet whose position is fixed not to follow the rotation of the photosensitive drum and which rotates,
This photoconductor has an electrode placed opposite to the magnet via a gap, magnetic powder is adsorbed between the photoconductor and the electrode, and a voltage is applied to the electrode to charge the photoconductor. Is an electrophotographic charging device.

Furthermore, the present invention provides a magnet A whose position is fixed.
And a rotating electrophotographic photosensitive member, and a magnet B having a magnetic force having a polarity opposite to that of the magnet A and having an electrode on the surface.
Is an electrophotographic charging device installed facing the magnet A with a gap between the photoconductor and the photoconductor, and magnetic force is attracted between the photoconductor and the electrode by the magnetic force of the magnet A and the magnet B, and the voltage is applied to the electrode. The electrophotographic charging device is characterized in that the photoconductor is charged by applying a voltage.

The present invention is also an electrophotographic charging device in which the voltage applied to the electrodes is a voltage obtained by superimposing a DC voltage on an AC voltage.

[0010]

In the present invention, since the magnetic binding force of the magnetic powder between the electrode and the photoconductor is increased by the above-described structure, (1) the magnetic powder is not carried away due to the electrostatic attraction of the photoconductor. (2) The magnetic powder adheres to the photoconductor due to the magnetic force, so that uniform and stable charging can be performed.

[0011]

EXAMPLES Zinc oxide, selenium, cadmium sulfide, amorphous silicon, phthalocyanine and azo pigment organic photoconductors can be used for the photoconductor used in the present invention. The surface of the photoconductor may be roughened by sandblasting or the like in order to accelerate the transportation of the developer layer.

The present invention uses an electrophotographic photosensitive drum containing a magnet. This magnet does not rotate but only the photoconductor rotates. At this time, if the magnet and the photoconductor are supported coaxially, there is an advantage that the mechanism for driving the photoconductor can be simplified and the magnetic pole position can be easily adjusted. The magnetic pole position of the magnet inside the photoconductor is, of course, the position before exposure.

The magnetic powder used in the present invention may be iron powder, magnetite or ferrite powder, nickel particles, or the like. They may be used as they are, or may be those whose surface is covered with iron oxide, or those which are covered with a high resistance material such as Teflon or silicon resin. The resistance value of the particles depends on the applied voltage, but is 10 ³ to 10 ⁸ Ωcm when a DC voltage is applied, and is 1 when an AC voltage is applied.
A resistance value of about 0 ⁷ to 10 ¹⁴ Ωcm is preferable. Further, the particle size was appropriately 10 μm to 200 μm. FIG. 2 shows the configuration of an electrode that faces the magnet of the photoconductor and carries the magnetic powder. Reference numeral 7 is a photoconductor drum, 8 is a magnet in the photoconductor 7, and an N pole is used here. Reference numeral 9 is a magnetic powder, 10 is an electrode for applying a voltage to the magnetic powder 9, 11 is a magnet located behind this electrode, and an S pole is used here. 12 is an electrode 1
A high-voltage power supply that applies a voltage to 0, and 13 is an elastic insulating sheet that prevents the magnetic powder 9 from spreading or being scattered by some impact. The electrode 10 is provided with a magnet 11 in the back here, but when iron powder or nickel powder having a high magnetic permeability is used, the magnet 11 may be omitted, and the magnet 11 may be made of a magnetic material. The magnet 11 is effective when it is desired to restrain the magnetic powder having a low magnetic permeability. The distance between the electrode 10 and the photoconductor 7 is 400 μm to 2 m.
It is installed about m away.

The high-voltage power supply 12 may apply a DC voltage when the surface potential setting of the photoconductor 7 is relatively low and the uniform charging is not required. For example, the absolute value of the voltage is about 100 to 1 kV. When it is desired to uniformly charge the photoconductor 7 at high speed, an AC power supply may be used as the high voltage power supply. The frequency of this AC voltage is
Approximately 2 depending on the image formation process speed
In the range 0 Hz to 2000 Hz, preferably 1
A range of 00 to 700 Hz is good. The value of the AC voltage is preferably a peak-to-peak value of about 1 kV. If the value of the DC voltage superimposed on the AC voltage is set to a value that is equal to the charging potential of the photoconductor and is several tens of percent higher than that, good charging can be obtained.

(Embodiment 1) Hereinafter, an electrophotographic charging device of the present invention will be described with reference to the drawings.

FIG. 1 shows an embodiment of the electrophotographic charging device of the present invention. In FIG. 1, 14 is an organic photosensitive drum in which phthalocyanine is dispersed in polyester binder resin, 15 and 16 are magnets fixed coaxially with the photosensitive body 14, 17 is an electrode for negatively charging the photosensitive body, 18
Is a magnet facing the magnet 16, 19 is a magnetic powder having a particle size of 30 μm and whose surface is coated with silicon, and 20 is an AC high-voltage power supply for applying a voltage to the electrode 17. The distance between the electrode 17 and the photoconductor 14 was set to 500 μm. Reference numeral 21 is a signal light, 22 is a developer reservoir, 23 is an insulating magnetic one-component developer, 24 is a non-magnetic electrode roller set with a gap of 300 μm from the photoconductor 14, and 25 is installed inside the electrode roller 24. A magnet, 26 an AC high voltage power source for applying a voltage to the electrode roller 24, 27 a scraper made of polyester film for scraping off the developer on the electrode roller, 28 a transfer corona charge for transferring the toner image on the photoconductor onto paper It is a vessel. Reference numeral 29 is a damper for smoothing the flow of the developer in the developer reservoir and for preventing the developer from being crushed by its own weight to cause clogging between the photoconductor and the electrode roller. The magnetic flux density on the surface of the photoconductor 14 by the magnet 16 is 80
It is 0 Gs. The magnetic flux density on the surface of the electrode 17 is 1000 Gs
Is. The width of the electrode 17 is 5 mm, and the diameter of the photoconductor 14 is 3
It is 0 mm. The photoconductor 14 was used by rotating it in the direction of the arrow in the figure at a peripheral speed of 60 mm / s. The diameter of the electrode roller 24 was 16 mm, and the electrode roller 24 was rotated at a peripheral speed of 40 mm / s in the direction opposite to the traveling direction of the photoconductor (the direction of the arrow in the figure). Photoconductor 1
The gap between No. 4 and the electrode roller 24 was set to 300 μm.

As the magnetic one-component developer, fine particle insulating magnetic one-component toner having a particle size of 5 μm was used. The composition of the magnetic one-component toner is 70% polyester resin, 25% ferrite,
Carbon black 3%, Oxycarboxylic acid metal complex 2%
Further, 1% of colloidal silica was externally added and used (all are% by weight).

The high voltage power source 20 is applied to the electrode 17 so that the frequency 1
30Hz, voltage 1.3kV (peak-to-peak),
When the superimposed DC voltage of -530V was applied, the photoconductor 14 was charged to -500V. The photoconductor 14 was irradiated with the laser beam 21 to form an electrostatic latent image. At this time, the exposure potential of the photoconductor was -90V. The toner 23 was magnetically attached to the surface of the photoconductor 14 in the developer reservoir 22. Next, the photoconductor 14 was passed in front of the electrode roller 24. When passing through the uncharged area of the photoconductor 14, the electrode roller 2
750V 0-p (peak-to-peak 1.5kV) superposed with 0V DC voltage by AC high-voltage power supply 26.
AC voltage (frequency 1 kHz) was applied. After that, −
When passing through the photoconductor 14 charged to 500V and having an electrostatic latent image written therein, 750V0-p (peak-to-peak 1.5kV, peak-to-peak 1.5kV) in which a DC voltage of -350V is superimposed on the electrode roller 24 by an AC high voltage power source 26. ) AC voltage (frequency 1
kHz) was applied. Then, the toner attached to the charged portion of the photoconductor 14 is collected by the electrode roller 24, and
A negative-positive inverted toner image remained only on the image portion on the upper portion. The toner attached to the electrode roller 24 rotating in the direction of the arrow was scraped off by the scraper 27, returned to the developer reservoir 224, and used for the next image formation. Developer reservoir 22
The state of toner circulation inside is shown by the dotted arrows. The toner image thus obtained on the photoconductor 14 is printed on paper (not shown).
After being transferred by the transfer charger 28, it was heat-fixed by a fixing device (not shown). As a result, the horizontal line is not disturbed and the toner is not scattered, the solid is uniform and the density is 1.5.
An extremely high-resolution and high-quality image in which an image line of 2 lines / mm was reproduced was obtained. At this time, almost no ozone generation was observed in the vicinity of the electrode 17.

[0019]

As described above, according to the present invention, since the magnetic binding force of the magnetic powder between the electrode and the photoconductor is increased, (1) the magnetic powder is carried away by losing the electrostatic attraction of the photoconductor. (2) Magnetic powder adheres to the photoconductor due to magnetic force for uniform and stable charging, and (3) Since the magnet on the electrode side does not need to be rotated, the device can be made smaller, resulting in a smaller size. Moreover, it is possible to obtain a charging device that produces a small amount of ozone and obtains high image quality.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an electrophotographic charging device according to an embodiment of the present invention.

FIG. 2 is an enlarged explanatory diagram illustrating in detail the configuration of the embodiment of the present invention.

FIG. 3 is a schematic view of a conventional electrophotographic charging device.

[Explanation of symbols]

 14 Photoreceptor 15/16/18/25 Magnet 17 Electrode 19 Magnetic Powder 20 High Voltage Power Supply 21 Laser Exposure

Claims (3)

[Claims] 1. A rotating electrophotographic photosensitive member containing a magnet whose position is fixed not to follow the rotation of the photosensitive drum.
An electrophotographic charging device having an electrode installed opposite to the magnet via a gap between the photosensitive member and the electrode, wherein magnetic powder is attracted between the photosensitive member and the electrode by the magnetic force of the magnet. An electrophotographic charging device characterized in that the photoreceptor is charged by applying a voltage to the photoconductor. 2. An electrophotographic photosensitive member which includes a magnet A whose position is fixed and rotates, and a magnet B which holds a magnetic force having a polarity opposite to that of the magnet A and which has an electrode on the surface thereof, are separated from the photosensitive member. An electrophotographic charging device is installed opposite to the magnet A via a magnet, wherein magnetic powder is attracted between the photoconductor and the electrode by the magnetic force of the magnet A and the magnet B, and a voltage is applied to the electrode. An electrophotographic charging device characterized in that the photoconductor is charged by being applied. 3. The electrophotographic charging device according to claim 1, wherein the voltage applied to the electrodes is a voltage obtained by superimposing a DC voltage on an AC voltage.