JP2000214656A - Image forming device and electrostatic charging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an excellent image by reducing an ozone evolution quantity, and permitting the highly efficient as well as uniform charge. SOLUTION: The image forming device has an electrostatic charging device 12 arranged in non-contact with a periphery of a photoreceptor drum 10 being an electrostatic latent image carrier, and the electrostatic charging device 12 is composed so that a discharging electrode 121 in a brush shape is located on a center of a housing opened at one end and moreover a grid member 123 is arranged in the opening part of the housing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus provided with a corona discharge type charging device,
In particular, the present invention relates to an image forming apparatus provided with a corona discharge type charging device using a non-contact type brush electrode and a charging device.

[0002]

2. Description of the Related Art Conventionally, in an electrophotographic image forming apparatus,
Charging devices used for charging the image carrier include:
There is something like.

A discharge wire type corona discharge device including a discharge wire 121 A, a back plate 122, and a grid member 123 shown in FIG. 8, a saw-tooth electrode 121 B and a back plate 1 shown in FIG.
22, a corona discharge device of a sawtooth electrode type comprising a grid member 123 and the like, and a charging device of a contact charging type using a roller or a brush.

The advantages and disadvantages of each are described as follows.

[0005] (Discharge wire method): It is possible to cope with high-speed image formation, and there is little charge unevenness and thus image unevenness. However, the amount of ozone generated is large due to poor discharge efficiency.

[0006] (Sawtooth electrode system): Applicable to high-speed image formation, and the amount of generated ozone is small. However, if the toner adheres to the teeth of the electrode, uneven charging is likely to occur,
Image unevenness due to charging unevenness is likely to occur.

(Contact charging method); Although the amount of generated ozone is small, it cannot cope with high-speed image formation.

[0008]

The above-mentioned conventional charging device has a problem that a large amount of ozone is generated when a high-speed image formation is enabled, and a problem that image unevenness occurs in a durable manner.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus and a charging apparatus which solve the above problems and have a high discharge capability, an excellent charging uniformity and a small amount of generated ozone.

[0010]

According to the present invention, there is provided an image forming apparatus comprising: a charging device disposed in non-contact with an electrostatic latent image carrier for holding an electrostatic latent image;
The image forming apparatus is characterized in that the charging device has a configuration in which a conductive brush is provided at the center of a housing having one end opened, and a grid member is provided at an opening of the housing. Achieved.

[0011] The charging device of the object is further characterized in that the housing has a conductive brush that is not in contact with a photoconductor that applies an electrostatic charge, a support that supports the brush, and a charge applying device that aligns the bristle tips of the brush. A charging device comprising: an area regulating member, wherein the support is configured to be bonded to a base of the brush via a conductive bonding agent; and A charging device including a conductive brush that is not in contact with a photoconductor that provides a charge, a support that supports the brush, and a charge application region regulating member that aligns the tips of the brush; Is achieved by a charging device having a configuration in which the brush is interposed and supported.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The construction and function of an image forming apparatus and a charging device of the present invention will be described with reference to FIGS.

(Embodiment 1) (Invention of Claim 1) In the image forming apparatus shown in FIG. 1, reference numeral 10 denotes a photosensitive drum which is an electrostatic latent image carrier, for example, an OPC photosensitive body is a conductive drum. The material applied on the top is grounded and is driven and rotated clockwise. Reference numeral 12 denotes a grid made of a stainless steel plate in which a brush-like discharge electrode 121 is provided at the center of a metal housing made of, for example, aluminum or stainless steel having one end opened, and the opening has a large number of holes formed by etching. 9 is a charging device of the present invention, which will be described after a configuration in which members are installed. In the present embodiment, a negative uniform charge is applied to the peripheral surface of the photosensitive drum 10 by corona discharge using a grid member and a corona discharge brush maintained at a predetermined potential, thereby giving a potential of V _H. Prior to the charging by the charging device 12, in order to remove the history of the photoconductor up to the previous print, exposure by the PCL 11 using a light emitting diode or the like is performed to eliminate the charge on the peripheral surface of the photoconductor.

After the photosensitive drum 10 is uniformly charged, the laser writing device 13 performs image exposure based on the image signal. In this image exposure, an image signal input from a computer or an image reading device is processed by an image signal processing section and then input to a laser writing device 13 to form an electrostatic latent image on the photosensitive drum 10.

The laser writing device 13 includes a rotating polygon mirror 13a which rotates by using a laser diode (not shown) as a light source.
The optical path is bent by a plurality of reflecting mirrors 13d through an fθ lens 13b and the like to perform main scanning.
An electrostatic latent image is formed by sub-scanning with a rotation of 0.
In this embodiment, the image portion is exposed based on the image signal, and the exposed portion forms a reversal latent image in which the absolute value of the potential is low V _L.

A developing device 14 containing a two-component developer composed of a negatively charged conductive toner and a magnetic carrier is provided around the periphery of the photosensitive drum 10, and has a magnet built in to hold the developer. The reversal development is performed by the rotating developing sleeve 14a.

The developer includes a carrier having ferrite as a core and an insulating resin coated around the core, and a toner containing a polyester or the like as a main material and a coloring agent such as a pigment or carbon black, a charge control agent, silica, titanium oxide or the like. And a carrier having a particle size of 10 to 50 μm and a saturation magnetization of 10 to 40 emu / g.
m, a toner having a charge amount of 5 to 20 μC / g
10% by weight of the developing sleeve 1
The layer 4a is conveyed to the developing zone while being regulated to a layer thickness of 0.1 to 0.6 mm.

The gap between the developing sleeve 14a and the photosensitive drum 10 in the developing zone is larger than the layer thickness of the developer.
As 2～1.0Mm, AC bias voltage obtained by superposing an AC voltage V _AC to a DC voltage V _DC is applied between the developing sleeve 141 and the photosensitive drum 10. Since charging of the toner is a DC voltage V _DC of the same polarity (negative), the toner given the opportunity to leave from the carrier by the AC voltage V _AC, the part of the high V _H absolute value of the potential from the DC voltage V _DC And the toner amount corresponding to the potential difference adheres to the portion of _VL where the absolute value of the potential is low, and visualization (reversal development) is performed. Further, only the DC voltage _VDC may be applied between the developing sleeve 14a and the photosensitive drum 10. The development may be contact development. The photosensitive drum 10 holding the toner image is transferred in the next transfer step.

On the other hand, the half-moon roller 1
The recording sheet P conveyed to the timing roller 15d via the transfer roller 5a and the conveyance rollers 15b and 15c is temporarily stopped, and the timing roller 15d is stopped when the transfer timing is adjusted.
Is fed to the transfer area 16b by the rotation operation of. In the transfer area 16b, a transfer roller 16a to which a high voltage having a polarity opposite to that of the toner is applied is pressed against the peripheral surface of the photosensitive drum 10 in synchronization with the transfer timing, and the fed recording paper P is pinched. As a result, the toner image on the peripheral surface of the photosensitive drum 10 is transferred onto the recording paper P.

Next, the recording paper P is discharged by the pointed electrodes 16c arranged with a slight gap, and the photosensitive drum 1
The transfer toner is conveyed to the fixing device 17 while being separated from the 0 peripheral surface, and the transfer toner is melted and fixed on the recording paper P by the heat and pressure of the heat roller 17a and the pressure roller 17b.
The sheets are discharged to the tray section 54 by 81 and 182. In addition,
The transfer roller 16a is retracted away from the peripheral surface of the photosensitive drum 10 from the time when the recording paper P has passed to the time when the next toner image is transferred.

On the other hand, the photosensitive drum 10 on which the toner image has been transferred onto the recording paper P is provided with a static eliminator 19 using an AC corona discharger.
After the static electricity is removed by the cleaning device 20, the residual toner remaining on the peripheral surface is scraped off by the cleaning blade 20 a made of a rubber material coming into contact with the photosensitive drum 10 to the cleaning device 20, and is discharged by the screw or the like. Or it is stored.

The photosensitive drum 10 from which residual toner has been removed by the cleaning device 20 is uniformly charged by the charging device 12 after being exposed by the PCL 11, and enters the next image forming cycle.

(Embodiment 2) (Invention of Claim 4) FIG. 2 is an enlarged sectional view showing the charging device 12 of FIG. In the figure, reference numeral 10 denotes the aforementioned photosensitive drum, 121 denotes a brush-like discharge electrode for corona discharge projecting toward the photosensitive drum 10, and 122 denotes a back plate 22a made of a metal such as aluminum, for example, by small screws 22c. A back plate 123, which is a housing having a U-shaped cross section and an opening, formed by attaching a stainless steel plate, is formed to a mesh pitch of 1 mm by etching a stainless steel plate having a thickness of 0.1 mm, for example. A grid member 124 installed in the opening of the back plate 122 is a charge made of an insulating material such as a synthetic resin that regulates a charge application range by arranging the tips of the brushes 12a on a straight line parallel to the rotation axis of the photosensitive drum 10. This is an application area regulating member.

The brush 12a is made of, for example, a conductive metal (for example, stainless steel) having a diameter of 100 μm, an amorphous metal,
Alternatively, the base 12b is made of semi-conductive fiber such as rayon, nylon, polyester or the like provided with conductivity.
As shown in FIG. 12, a cloth-like substrate 12c made of conductive fibers implanted with 4 to 6 brushes 12a at intervals of 1 mm.
Reference numeral 125 denotes a conductive adhesive, and reference numeral 125 denotes a support obtained by integrally bonding a conductive support A25a made of aluminum or the like and a support B25b made of an insulating material such as a synthetic resin with an adhesive or a small screw. The back surface of the cloth-like base 12b is electrically conductive with an electrically conductive support 12A by an electrically conductive adhesive 12c.
And electrically connected.

Reference numeral 126 denotes a flicker bar for cleaning the brush 12a, for example, a bar-shaped synthetic resin having a diameter of 4 mm.
Reference numeral 7 denotes a duct for sucking toner generated when the brush 12a is cleaned by the flicker bar 126 through a number of holes 22b formed in the back plate 22a of the back plate 122 by a fan (not shown). The flicker bar 126 is moved by, for example, a drive unit provided separately in front and rear of the drum axis direction in FIG. 2 every 1,000 prints, and rubs the bristle tip of the brush 12a to remove the attached toner. Evacuate to

The base of the base 12b of the brush 12a is aligned by the charge applying region regulating member 124, and the bristle protrudes from the tip of the charge applying region regulating member 124 by about 3 mm. It is fixed to the support 125 by the agent 12c. As shown in FIG. 4, the distance between the brushes 12a is D = 1 mm by the charge application region regulating member 124.
At a position parallel to the rotation axis of the photosensitive drum 10 and a diameter of 1
In the case of a brush group using six 00 μm fibers, the gap d ₁ between the brush groups 12 d is about 400 μm. If the interval D between the brush groups 12d is 4.5 mm or less, there is no problem in performing uniform charging.

For example, as shown in FIG. 2, the support 125 has a back plate
Although it is attached inside 2b, it can be configured to be attached with screws and fasteners.

FIG. 5 is a perspective view showing an example of a method for attaching the grid member to the back plate. Locking claws 122a are provided at four corners of the opening of the back plate 122, and small holes 123a are provided at one corner of the grid member 123.
However, a small hole 123b is formed near the corner at the other end, and one end of a spring material 123c having an arc-shaped locking portion formed at both ends is hung on the small hole 123b. Grid member 1
After locking the small hole 123a at one end of the back plate 122 with the locking claw 122a at one end of the back plate 122, the grid member 123
The other end of the spring member 123c attached to the other end of the back plate 122 is engaged with the engaging claw 122a at the other end of the back plate 122, and the grid member 123 is attached to the back plate 122 by the tension of the spring member 123c. With this configuration, the position of the grid member 123 is regulated by the back plate 122, and electrical connection is made.

The grid member 123 of the charging device 12 having the brush-shaped discharge electrode 121 and the photosensitive drum 10
Is maintained so as to always maintain a predetermined gap (for example, 1 mm).

The discharge electrode 121 of the charging device 12 includes:
Under the control of a control unit (not shown), if the photosensitive drum 10 is charged to a potential of -750 V at the time of charging, for example, the discharge electrode 121 is determined by the charging condition by the AC power supply E1. For example, an AC voltage having a peak-to-peak voltage (V _PP ) controlled at a constant current of 800 μA = 4 to 6 kV and a frequency of 1 to 4 kHz is applied via the power supply unit 25 d of the support 125 via the capacitor C, and the back plate 122 and the The grid member 123 is supplied with a bias voltage of -750 V, which is controlled at a constant voltage by the DC power supply E2.
It is applied via 2d. The voltage applied by the discharge electrode 121 may be a DC power supply.

The cleaning of the brush 12a is performed by the flicker bar 12.
6 is performed. As a durability test, the inventor moved the flicker bar 126 at a speed of 10 mm / sec.
Approximately 5,000 when the bite amount into the brush 12a is 2 mm
The tip of the brush 12a was rubbed 0 times, but the fall of the brush 12a was 1 to 1.5 mm. No discharge unevenness occurred with the amount of the brush falling.

(Embodiment 3) (Invention 5) FIG. 6 is a sectional view showing another embodiment of the charging device of the present invention.

The same reference numerals as in FIG. 2 denote the same parts in the respective parts, and the operation is also the same. In the drawing, 12f is a charge-applying region regulating member having a hairpin-shaped cross-section made of a spring material such as a phosphor bronze plate having a spring property to be sandwiched with conductivity, and 125 is a U-shaped groove 25g at the center. Is a support body in which a conductive support body A25a on which is formed and an insulative support body B25b having a dovetail groove are integrally joined by a small screw 25c or an adhesive. The brush 12a implanted in the narrow base 12b is a charge application region regulating member 12f.
After the bristle tips are supported in a state close to one row, the bristle tips are aligned in parallel with the rotation axis of the photosensitive drum 10, and the bottom portion, which is the curved portion of the charge applying region regulating member 12 f, is conductively bonded. It is configured to adhere to the groove 25g of the support A by the agent 12c and to be integrated with the support 125.

The discharge electrode 121 is connected to an AC power source E1
Peak-to-peak voltage (V
_PP ) = AC voltage of 4 to 6 kV, frequency of 1 to 4 kHz is applied via the power supply part 25 d of the support A 25 a via the capacitor C, and the back plate 122 and the grid member 1
23 has a constant voltage of -750 controlled by the DC power source E2.
A bias voltage of V is applied via the power supply unit 22d. Also in the present embodiment, a DC power supply may be used for discharge pole 121.

(Comparative Experiment) Using the image forming apparatus shown in FIG. 1 provided with the charging device 12 shown in the second or third embodiment as an example, the charging device 1 of the image forming apparatus shown in FIG.
Comparative Example 1 is an image forming apparatus in which the charging device 12 is replaced with a discharging wire type charging device (FIG. 8), and Comparative Example 2 is an image forming device in which the charging device 12 is replaced with a sawtooth electrode type charging device (FIG. 9). In each of the examples, a halftone image was formed, and the change in the surface potential of the photoconductor relative to the copy number (potential change) was measured.

The charging and image forming conditions in each example are as follows: Photoreceptor linear velocity: 280 mm / sec (photoreceptor diameter 80 mm) Applied voltage to grid member: -750 V (constant voltage) Applied voltage to back plate: -750 V (constant voltage) Voltage) Applied voltage (AC voltage) of discharge electrode: V _PP = 4 to 6 k
V, frequency 1 to 4 kHz (constant current of -800 μA) Distance between grid member and photoconductor: 1.0 mm Photoconductor charging potential: -750 V Here, the photoconductor is a photoconductor layer formed on the surface of photoconductor drum 10. That is.

In the embodiment, the brush 12a is made of amorphous metal fiber Volfa DE-10 (made by Unitika), and the distance between the tip of the brush 12a and the grid member 123 is 3.0 mm.

In Comparative Example 1, the discharge wire 121A has a diameter of 6
A gold plated wire of 0 μm is used, and the distance between the wire 121A and the grid member 123 is 7.5 mm.

In Comparative Example 2, the sawtooth electrode 121B has a sawtooth pitch of 2 mm, and the distance between the tip of the sawtooth electrode 121B and the grid member 123 is 7.5 mm.

In any case, no feedback is made by the potential sensor.

Under the above conditions, without cleaning the discharge electrode,
000 times of copying, the amount of generated ozone was determined by measuring the ozone concentration near the charging device, and the charging unevenness was determined by the density unevenness of the halftone image.

[0042]

[Table 1]

As shown in Table 1, in the image forming apparatus and the charging device of the present invention, there was no uneven charging, and the amount of generated ozone was
It has been found that the charging device is about 1/5 of the discharge wire type charging device and almost the same as the serrated electrode type charging device.

FIG. 7 shows the change in the surface potential of the photoconductor depending on the copy number, and the charging performance obtained by the potential measurement was almost the same. However, in the case of the charging device of the sawtooth electrode type, a large number of stripes (white stripes) were observed on the recording paper, but in this embodiment, almost no unevenness was observed.

Although the above description has been made on the case where the present invention is applied to an image forming apparatus of a type in which exposure is performed from the outside of a normal photosensitive drum 10, the present invention is also applicable to an image forming apparatus of a type in which exposure is performed from the inside of the apparatus. Of course.

Although the image forming apparatus according to the present invention has been described as having a drum-shaped image forming body, it is needless to say that the present invention can be applied to an apparatus having a belt-shaped image forming body for forming an image.

[0047]

As described above, according to the present invention, the brush-like discharge electrode and the charge-applying region regulating member dispose the brush tips in a concentrated manner, thereby preventing the occurrence of uneven discharge. It has become possible to provide an image forming apparatus and a charging apparatus capable of improving charging efficiency, thereby enabling high-speed image formation, reducing the amount of generated ozone, performing stable and uniform charging, and obtaining high-quality images. .

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a configuration of an image forming apparatus of the present invention.

FIG. 2 is an enlarged sectional view showing an embodiment of the charging device of the present invention.

3 is a cross-sectional view illustrating an example of a brush and a base of a discharge electrode of the charging device of FIG. 2;

FIG. 4 is a plan view showing a result of brushes being aligned by a charge application region regulating member.

FIG. 5 is a perspective view illustrating an example of a method of attaching a grid member of the charging device of FIG. 2;

FIG. 6 is a sectional view showing another embodiment of the charging device of the present invention.

FIG. 7 is a graph showing transition of a charging potential by the present invention and a conventional charging device.

FIG. 8 is a longitudinal sectional view showing a charging device of a discharge wire system.

FIG. 9 is a longitudinal sectional view showing a charging device of a sawtooth discharge electrode system.

[Explanation of symbols]

 REFERENCE SIGNS LIST 10 photoconductor drum (electrostatic latent image carrier) 11 PCL 12 charging device 13 laser writing device 14 developing device 20 cleaning device 121 discharge electrode 122 back plate (housing) 123 grid members 124, 12 f charge application region regulating member 125 support 126 Flicker bar 127 Duct E1 AC power supply E2 DC power supply

Claims (6)

[Claims] 1. An image forming apparatus having a charging device arranged to be in non-contact with an electrostatic latent image carrier for holding an electrostatic latent image, wherein the charging device is located at a center of a housing having one end opened. An image forming apparatus, wherein a conductive brush is provided, and a grid member is provided at an opening of the housing. 2. The image forming apparatus according to claim 1, wherein said housing is made of metal. 3. The image forming apparatus according to claim 1, wherein the grid member is a member formed by etching. 4. A housing comprising: a conductive brush that is not in contact with a photoconductor that applies an electrostatic charge; a support that supports the brush; and a charge application region regulating member that aligns the brush tips of the brush. A charging device, wherein the support is configured to be bonded to a base of the brush via a conductive bonding agent. 5. A housing comprising: a conductive brush that is not in contact with a photoconductor that applies an electrostatic charge; a support that supports the brush; and a charge application region regulating member that aligns the bristle tips of the brush. A charging device, wherein the support is configured to support the brush with the brush interposed therebetween. 6. The charging device according to claim 4, wherein a current is supplied from the support to the brush.