JPH04343373A - Contact type electrostatic charger - Google Patents

Abstract

PURPOSE:To almost remove the noise generated in electrostatically charging, to secure that the electrostatic charging blade may be made to stably abut on the body to be charged in the case of a long use, and to uniformly charge it with stability in a contact type electrostatic charger using an electrostatic charging blade as an electrostatic charging member, impressing an oscillating voltage on the electrostatic charging blade, and electrostatically charging a body to be electrostatically charged. CONSTITUTION:As to the contact type electrostatic charger for making the electrostatic charging member 10 on which the oscillating voltage is impressed come into contact with the body 1 to be charged so as to charge the body 1 the electrostatic charging member 10 is formed to the shape of a blade and supported so as to freely rock and also is brought into press-contact with the body 1 to be charged by a press-contact means 24.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a contact charging device that charges (including neutralizes) the surface of a charged object by bringing a charging member to which a voltage is applied into contact with the charged object.

0002

2. Description of the Related Art Conventionally, as a means for uniformly charging the surface of an image bearing member such as a photoconductor or dielectric material as a charged member in an image forming apparatus such as a copying machine or a recording device, a corotron with good uniform charging property has been used. Corona dischargers such as scorotrons and scorotrons are widely used.

However, corona dischargers require an expensive high-voltage power source, require space for themselves and the shield space for the high-voltage power source, and often generate corona products such as ozone, which require additional equipment to deal with them. It has problems such as requiring means and mechanisms, which make the device larger and more expensive.

[0004] Therefore, in recent years, consideration has been given to adopting a contact charging type device in place of the corona discharger, which has many of the problems mentioned above. In contact charging, a contact charging member (conductive member) to which a voltage is applied is brought into contact with the surface of the image carrier, which is the object to be charged.
The image carrier surface is charged to a predetermined potential, and roller charging type (JP-A-56-91253) and blade charging type (JP-A-56-194349 and JP-A-60-14) are used.
7756 (Japanese Patent Application Laid-Open No. 165166), and a charging/cleaning type (Japanese Unexamined Patent Publication No. 165166/1983) have been devised.

The voltage applied to the charging member is generally only a DC (direct current) voltage of 1 to 2 KV;
As disclosed in Japanese Unexamined Patent Publication No. 63-149669, there is a device that applies an oscillating voltage, for example, a superimposed voltage of an AC (alternating current) voltage and a DC voltage.

[0006] The former type of contact charging, which applies only a DC voltage, has the advantage that the applied voltage is low and a simple and inexpensive power source can be used, but on the other hand, it tends to cause spot-like charging unevenness, and it also causes damage to the charging member. It is sensitive to dirt, etc. and has a small latitude for uniform charging.

On the other hand, the latter type of contact charging, which applies an oscillating voltage, can significantly improve spot-like charging unevenness, and requires a slightly more complicated power source and higher cost than contact charging, which applies only a DC voltage. However, the latitude for achieving uniform charging properties is large. The oscillating voltage is disclosed in Japanese Patent Application Laid-Open No. 63-14
As disclosed in Japanese Patent No. 9669, an oscillating voltage in which an AC voltage having a peak-to-peak voltage that is at least twice the charging start voltage of the charged object is superimposed on a DC voltage is effective.

[0008]

[Problems to be Solved by the Invention] However, in the case of contact charging in which an oscillating voltage is applied, the applied oscillating voltage causes the charging member to vibrate, and the object to be charged, to which the charging member is pressed, also vibrates, causing so-called The drawback was that it produced a "charging noise."

This charging sound has a frequency that is, for example, twice the frequency of the AC voltage component of the oscillating voltage applied to the charging member, and the frequency of the applied voltage is low (for example, 200 Hz).
(below), the sound does not give the impression of being harsh and unpleasant, but as the frequency is raised, it gradually becomes harsh and unpleasant. Therefore, in order to prevent the charging sound from bothering the ears, it is desirable to set the frequency to 200 Hz or less.

[0010] However, if the frequency is too low, in the image forming apparatus, in halftone images, [process speed (mm/sec)/frequency (Hz)] m
Pitch unevenness of m occurs. This pitch unevenness is 0.1mm
If it is only 0.15m, it cannot be seen with the naked eye.
If the pitch is greater than m, it will be visible to the naked eye, which is undesirable in terms of image quality.

[0011] Considering the above points, the process speed at which pitch unevenness is not discernible and charging noise is not felt at a frequency of 200 Hz or less must be at least 30 mm/sec or less. However, in reality, most electrophotographic equipment has a process speed of 30 mm/sec.
As described above, in an image forming apparatus having this process speed, when using contact charging in which the above-mentioned oscillating voltage is applied, it is necessary to reduce the charging noise by some means or to make it less harsh.

[0012] The charging sound also changes depending on the shape and material of the charging member, and when the charging member is blade-shaped (hereinafter referred to as charging blade) and is fixed to the object to be charged,
Charging noise tends to be louder than a roller-shaped charging member that rotates relative to the object to be charged.

FIG. 5 is a schematic diagram of a conventional contact charging device using a charging blade as a charging member. 1 is an object to be charged. This example is a photosensitive drum of an electrophotographic apparatus, which is rotated in a clockwise direction A as indicated by an arrow at a predetermined process speed (peripheral speed).

Reference numeral 10 denotes a charging blade made of, for example, conductive rubber and whose resistance value is controlled. The charging blade 10 is attached to and supported by a blade support sheet metal 16, and the blade support sheet metal 16 is held against the immovable member 50 with the tip of the blade pressed against the surface of the photosensitive drum as a charged object with a predetermined contact pressure. It is fixed.

In this example, the charging blade 10 is connected to the photosensitive drum 1.
θ° with respect to the tangent O at a position α° from the horizontal direction of
The photosensitive drum is brought into contact with the rotation of the photosensitive drum in a counter direction with a contact angle of . The charging blade 10 has its back electrode 21 electrically connected to a conductive blade support plate 16 via a conductive paint 22.
By applying a predetermined oscillating voltage from the power source E, power is supplied to the charging blade 10, and the peripheral surface of the rotating photosensitive drum 1 is charged in a contact manner. L is the free length of the blade from the tip a of the blade support sheet metal 16 to the tip of the charged blade.

[0016] The charging noise tends to be louder as the amount of penetration of the charging blade increases and as the nip width w between the charging blade and the object to be charged increases. On the other hand, when bringing the charging blade into pressure contact with the charged object, a certain amount of pressure is necessary, and the amount of penetration is 0.3
I want to ensure the degree. Considering this variation in the amount of penetration,
0.7 may be produced, and in this case, charging noise was a major problem.

Therefore, the present invention provides a contact charging device that uses a charging blade as a charging member and applies an oscillating voltage to the charging blade to charge an object to be charged. The object of the present invention is to ensure stable contact with a charged object and to stably perform uniform charging.

[0018]

[Means for Solving the Problems] The present invention is a contact charging device characterized by the following configuration.

(1) In a contact charging device that charges an object to be charged by bringing a charging member to which an oscillating voltage is applied into contact with the object to be charged, the charging member has a blade shape and is supported so as to be swingable; A contact charging device characterized in that it is pressed into contact with an object to be charged by a pressure contact means.

(2) The contact according to (1), wherein the oscillating voltage is a superimposed voltage of an AC voltage having a peak-to-peak voltage that is at least twice the charging start voltage of the charged object and a DC voltage. Charging device.

(3) The contact charging device according to (1), wherein the blade-shaped charging member also serves as a cleaning blade for the object to be charged.

[0022]

[Function] When the charging blade is arranged as described above, as shown in the example below, the charging noise generated is actually reduced, and the contact charging blade as a charging member and the object to be charged are stabilized over a long period of time. This makes it possible to maintain a contact state in which the contact state of contact is maintained, making it possible to realize a contact charging device with a wider manufacturing latitude. Further, even in a faster-speed image forming apparatus, it was possible to stably perform the charging process on the image bearing member as the charged member using the charging blade.

Furthermore, in an image forming apparatus, by using the charging blade also as a cleaning blade for the image bearing member, which is a charged object, an image forming apparatus and a process cartridge can be constructed more easily, at a lower cost, and in a smaller space. It becomes possible to do so.

[0024] The reason why image unevenness worsens after durability in an image forming apparatus is considered to be that the contact pressure decreases due to fatigue of the charging blade, causing contact unevenness, which worsens image unevenness. It will be done. According to the charging device configuration of the present invention, a contact pressure of 40 g/cm or less is sufficient for charging noise, and if the contact pressure is 5 g/cm or more, image unevenness after durability is almost good, and the contact pressure can be set in a very wide range. The reason why the image unevenness does not deteriorate much even after durability is thought to be that even if the charging blade becomes stale, the pressure contact means ensures that the charging blade maintains good contact with the charged object, making contact unevenness less likely to occur. It will be done.

[0025]

【Example】

<Example 1> (FIGS. 1 and 2) (1) Image forming apparatus FIG. 1 is a schematic diagram of the main parts of an image forming apparatus using a contact charging device according to the present invention.

1 is a rotating photosensitive drum (electrophotographic photosensitive member, this example is an OP with a thickness of 25 μm and a dielectric constant of about 3) as an image carrier.
A C photosensitive layer 1a is formed on a conductive drum base 1b made of Al), and is rotated in a clockwise direction A as indicated by an arrow at a predetermined process speed. In this embodiment, the image carrier 1 is of a drum type, but it may be of a rotary belt type or the like. In either case, a seamless type can of course be used, and a seamed type can also be used if a synchronization signal is obtained and each copying process is performed.

2 is a short focus lens array as an exposure means for forming a latent image on the photosensitive drum 1; 3 is a developing device; 4 is a transfer roller as a transfer means; The transfer material P conveyed sheet by sheet is synchronized with the rotation of the photosensitive drum 1, and the transfer material P is transferred between the photosensitive drum 1 and the transfer roller 4 (
A timing roller (registration roller) 7 is a transfer guide disposed between the timing roller 6 and the transfer roller 4 and serves as a guide for the transfer material P.

Reference numeral 8 denotes a conveyance unit that passes between the photosensitive drum 1 and the transfer roller 4 and introduces the transfer material P on which the image has been transferred to a fixing device (not shown); 9 carries the remaining material on the photosensitive drum 1 after the image transfer; A cleaning device for removing toner, etc., 9a is a cleaning blade, and 10 is a charging blade as a charging member that contacts the photosensitive drum 1 after cleaning to uniformly charge the photosensitive drum 1; this charging blade 10 will be described later. do.

The image forming apparatus of this example includes a photosensitive drum 1, a developing device 3, a cleaning device 9, and a charging blade 10.
A process cartridge 2 in which two process devices are assembled together in a predetermined positional relationship with each other.
0, and this cartridge 20 can be inserted into the main body of the image forming apparatus along a support rail (not shown) in a direction perpendicular to the drawing, and conversely can be freely removed from the main body of the apparatus. It is. By fully inserting and mounting the process cartridge 20 into the apparatus main body, the apparatus main body side and the process cartridge 20 side are mechanically and electrically coupled to each other, and the image forming apparatus becomes operable.

(2) Charging blade 10 FIG. 2 is an enlarged view of the charging blade 10 portion.

The charging blade 10 is fixedly supported on one arm plate side of a blade support metal plate 15 that can freely swing around a support shaft 23. The blade support sheet metal 15 is the charged blade 1
The other arm plate on the opposite side to the arm plate side on which 0 is fixedly supported,
Support shaft 2
The charging blade 10 is constantly urged to rotate in the counterclockwise direction B around the charging blade 3, so that the leading end of the charging blade 10 abuts against the photosensitive drum 1 and is maintained in pressure contact with the photosensitive drum 1.

In this embodiment, the charging blade 10 contacts the photosensitive drum 1, which is the object to be charged, at a position of α° in the horizontal direction and at an angle of contact of θ° with respect to the tangent (the blade tip and the blade contact the drum). The blade is brought into contact with the rotation of the photosensitive drum 1 in the counter direction (the contact angle is an acute angle) at the angle formed by the line on the downstream side of the drum movement direction from the blade contact point among the tangent lines of the drum at the contact point. There is.

The contact position angle α° is appropriately selected depending on the arrangement of each process device and the diameter of the photosensitive drum used. The contact angle θ° of the charging blade 10 is desirably 30° or less in terms of charging stability. Although the direction of contact is not limited to the counter, counter contact is better than forward contact (obtuse contact angle) even if toner or other residue reaches the blade edge. Counter abutment is more desirable because the residue is dammed up and difficult to reach the charged surface on the downstream side of the edge portion in the direction of movement of the drum surface, making it less likely that uneven charging will occur.

A back electrode 21 is provided on the back side of the charging blade 10 opposite to the photosensitive drum contact side, and is electrically connected to the charging blade 10.
The voltage applied from the power source E to the charging blade 10 is applied to the conductive blade support plate 15 and then to the blade support plate 15.
The electric current is applied to the charging blade 10 through the conductive paint 22 that electrically connects the back electrode 21 and the back electrode 21, and finally through the back electrode 21.

The pressing force of the charging blade 10 against the photosensitive drum 1 can be adjusted by changing the spring constant of the pressing spring 24. As for the pressing force, a linear pressure of the charging blade 10 of 5 g/cm to 40 g/cm is appropriate. If the linear pressure is less than 5 g/cm, uneven contact in the longitudinal direction is likely to occur, although it depends on the edge precision of the charging blade 10 and the degree of waviness, and in areas with poor contact, halftones may appear on the image. There is an inconvenience that spotty uneven charging occurs. Furthermore, when the linear pressure exceeds 40 g/cm, the charging sound becomes harsh, the charging blade 10 is greatly worn, the wear scratches on the photosensitive drum 1 are also large, and the driving torque of the photosensitive drum 1 is also increased. It's inconvenient.

The charging blade 10 has a medium resistance layer 10a.
It consists of two layers: and a coating layer 10b. The voltage applied to the back electrode 21 is applied to the microscopic gap formed between the photosensitive drum 1 as the object to be charged and the charging blade 10 via the medium resistance layer 10a and the coating layer 10b of the charging blade 10. This will create the necessary electric field.

The medium resistance layer 10a is made by adding conductive powder such as carbon black or metal oxide (zinc oxide, titanium oxide) to a rubber such as epichlorohydrin rubber or EPDM, and thereby increasing the volume resistivity to 1×10 6 to 1×10 9 . The thickness is controlled to Ωcm, and the appropriate thickness is about 1 to 3 mm.

The coating layer 10b has a surface resistance of 5×10 7
It can be used if it is Ω/mouth or more, and the thickness is 3 to 100 μm.
That's about it. If the thickness is less than 5 μm, there will be almost no coated portions due to unevenness in the coating thickness, so in terms of coating stability, the thickness of the coating layer is preferably 10 μm or more, including the uneven thickness. The material for the coating layer 10b is preferably one that is flexible, has excellent surface properties, has a low coefficient of friction, and has wear resistance.

In this example, PTFE dispersion paint (
Carbon is dispersed in Emlaron 345 (product name: Nippon Acheson Co., Ltd.) to increase the surface resistance to 1.7 x 108 Ω/port (1
．． 0 KV) was adjusted to 1 x 108 Ωcm (1
Medium resistance layer 1 with volume resistance adjusted (when applying 000VDC)
0a, coat 10b with a thickness of 30 μm by dipping.
The charged blade 10 was used.

The coating layer 10b has a much lower coefficient of friction than the epichlorohydrin rubber of the medium resistance layer 10a, and has significantly improved slip properties, so that it can prevent the so-called "blade turning" phenomenon at the initial stage of rotation of the photosensitive drum 1. It is very effective in reducing the torque caused by the blade pressure force and reducing the occurrence of drum scratches due to durability.

In this embodiment, the charging blade 10 has a two-layer structure, and the surface resistance of the medium resistance layer 10a is 5×1.
If it is 07 Ω/mouth or more, has a low coefficient of friction, and does not cause "blade turning" etc., coat layer 1
Needless to say, it is not necessary to provide 0b, and a charging blade with only one layer may be used.

The charging sound and image characteristics of the charging device of this embodiment (FIGS. 1 and 2) and the conventional charging device of FIG. 5 were investigated under the same contact conditions below (however, the contact pressure,
(The amount of penetration is varied).

<Contact conditions> α°=35°θ°=15° Thickness t of charging blade 10 = 1.5 mm Free length L of blade 10 = 6.5 mm <Image output conditions> Process speed 72 mm/sec Exposure Drum diameter φ30 Applied bias AC+DC AC 500Hz, 1800Vpp DC -750V Pre-exposure No potential setting Dark area VD = -700V Bright area VL = -230V Halftone area VH = -400V The results are shown in Table 1. Regarding image unevenness, halftone images were evaluated at the initial stage and after running for 3K sheets.

[0044]
Table 1 No. Contact pressure
Charging sound Initial image unevenness Image unevenness after durability Book 1 5g/cm
〇 〇
〇△ Fruit 2 10g/c
m 〇 〇
〇 3 30
g/cm 〇 〇
〇 Example 4
40g/cm 〇△ 〇
〇 Submissive 1
Intrusion amount 0.2mm 〇 △
× Come 2
0.3mm 〇
〇 × Example
3 0.5mm 〇△
〇 〇△
4 0.8mm ×
〇 〇
Charging sound 〇……
almost inaudible
〇△…Can be heard faintly
×……
Uneven image that is harsh on the ears 〇...OK
〇△…Sometimes minor things occur.

△……Minor
×...NG (Terrible) From Table 1, in the conventional example, in order to reduce the charging noise to a certain level, the penetration amount must be 0.5 or less, and in order to improve the image unevenness after durability. It is desirable that the amount of penetration is 0.5 or more, and the amount of penetration that satisfies both of these is in a very narrow range around 0.5.

The reason why the image unevenness becomes worse after the durability test compared to the initial state is that the contact pressure decreases due to the charging blade 10 becoming worn out, which causes contact unevenness and worsens the image unevenness. Conceivable. On the other hand, in this embodiment, a contact pressure of 40 g/cm or less is sufficient for the charging noise, and if the contact pressure is 5 g/cm or more, the image unevenness after durability is almost good. It is now possible to set the contact pressure within a very wide range.

In this embodiment, the reason why the image unevenness does not deteriorate much even after durability is that even if the charging blade 10 becomes sag, the contact pressure is guaranteed by the pressure spring 24 of the charging blade 10. This is thought to be because uneven contact is less likely to occur. The electrical characteristics of the charging blade 10 must be set to a narrow range of medium resistance, and it is necessary to add conductive powder to impart conductivity. Furthermore, since the resistance value range is narrow, it is not possible to expect a significant change in the rubber formulation. Therefore, it is difficult to significantly improve the creep characteristics by reducing the settling of the charging blade 10. Considering the above, the configuration of this embodiment has the advantage that only the electrical characteristics of the charging blade can be determined mainly by the rubber formulation.

Note that as the waveform of the AC voltage component of the applied voltage, a sine wave, a rectangular wave, a triangular wave, etc. can be used as appropriate. Further, the alternating current voltage includes, for example, a rectangular wave voltage formed by periodically turning on and off a direct current power source. In this way, the AC voltage is a voltage whose voltage value changes periodically.

<Embodiment 2> (FIG. 3) FIG. 3 is a schematic configuration diagram of a second embodiment.

[0049] The charging device of the first embodiment described above differs only in the pressurizing means for the charging blade 10, and the other configurations are exactly the same. That is, in the first embodiment, the pressure spring 24 serving as the pressure means was a tension coil spring, and thus the spring 24 was designed only to pressurize the charging blade 10. Therefore, an electrode for applying voltage to the charging blade 10 or a contact point for receiving power from the main body of the image forming apparatus is required.

In this embodiment, the primary charging contact 26 that receives power from the main body of the image forming apparatus is made of a plate spring and fixed to the cartridge frame 28, and this plate spring is connected to the outside of the process cartridge 20 as a power receiving contact. A portion 26a is exposed, and a leaf spring part 26b is inserted into the interior as a pressurizing means for rotationally biasing the blade support sheet metal 15, and its tip is brought into contact with the blade support sheet metal 15 to apply pressure and support the blade. The sheet metal 15 is rotated and biased in the counterclockwise direction B around the support shaft 23 to bring the tip of the charging blade 10 into contact with the photosensitive drum 1 with a predetermined pressure, and at the same time, the voltage necessary for charging is applied to the photosensitive drum 1. Next, a voltage is applied from the charging contact 26a to the charging blade support metal plate 15 via the leaf spring portion 26b.

As in this embodiment, the primary charging contact 26, which is fixed to the cartridge frame 28 and makes contact with the power supply system of the image forming apparatus for electrical connection, has a leaf spring configuration.
It becomes possible to construct the pressure means and the voltage supply means of the charging blade 10 from the same member.

Embodiment 3 (FIG. 4) FIG. 4 is a schematic diagram of the third embodiment. In this embodiment, the charging blade 10 is also used as the cleaning blade of the cleaning device 9.

The charging blade 10 is located at the upper opening of the cleaning device 9, and forms the cleaning device 9 together with the charging blade 10, the charging blade support plate 15, the sealing member 31, the cleaning container 9b, and the scooping sheet 9c. The charging blade 10 also serves as a cleaning blade for removing transfer residual toner on the photosensitive drum 1.

The charging blade 10 is fixedly supported on one arm plate side of a blade support metal plate 15 that can freely swing around a support shaft 23. The pressure spring 30 of the charging blade 10 is a conductive compression spring inserted between the other arm plate of the blade support plate 15 and an electrode plate 32 provided on the inner surface of the process cartridge frame 28. The support metal plate 15 is constantly urged to rotate in the counterclockwise direction B around the support shaft 23, so that the tip of the charging blade 10 is maintained in abutting contact with the photosensitive drum 1. Voltage is applied from the power source E to the charging blade 10 through the electrode plate 32.
, conductive compression spring 30 , conductive rail support sheet metal 15
, conductive paint 22 and back electrode 21. The sealing member 31 is fixed to the upper end of the cleaning container 9b, and prevents toner from leaking from the cleaning device 9 by eliminating the gap between the blade support plate 15 and the container 9b.

In this embodiment, the contact pressure of the charging blade 10 against the photosensitive drum 1 is desirably 20 g/cm or more since cleaning performance is also required. Since the charging blade 10 also serves as a cleaning blade, there is no need for a cleaning blade, the process cartridge can be configured more easily, and there is an advantage that a low-cost, space-saving process cartridge can be provided. Furthermore, by cleaning with a blade to which an AC voltage is applied, toner strongly adhered to the surface of the photosensitive drum due to Coulomb force is also neutralized or charged to the opposite polarity, and a greater cleaning effect can be expected.

[0056] Compared to the urethane rubber etc. conventionally used in cleaning blades, the charging blade uses rubber that has a large degree of settling, but by adopting the configuration of this embodiment, fluctuations in contact pressure can be reduced. stable contact,
Cleanability can be ensured. In order to reduce the settling, the coating layer 10b of the charging blade is
It is preferable to provide it only at the tip. This is because the coating layer 10b is made of many materials that have higher hardness than the medium resistance layer 10a and do not exhibit rubber properties.

[0057]

As described above, according to the present invention, there is almost no charging noise in a contact charging device that uses a charging blade as a charging member and applies an oscillating voltage to the charging blade to charge a charged object. Moreover, stable contact of the charging blade with the object to be charged is ensured during long-term use, and uniform charging can be stably performed.

[Brief explanation of the drawing]

FIG. 1 A schematic configuration diagram of the main parts of an image forming apparatus using a contact charging device according to the present invention.

[Figure 2] Enlarged view of contact charging device part

[Figure 3] Schematic configuration diagram of main parts of the second embodiment device

[Figure 4] Schematic configuration diagram of main parts of the third embodiment device

[Figure 5] Schematic diagram of a conventional contact charging device

[Explanation of symbols]

1 Photosensitive drum 10 as a charged object Charging blades 24, 26, 30 Pressure spring or compression spring as pressure contact means

Claims (3)

[Claims] 1. In a contact charging device that charges a charged object by bringing a charging member to which an oscillating voltage is applied into contact with the charged object, the charging member has a blade shape, is supported in a swingable manner, and is press-contacted. A contact charging device characterized in that it is brought into pressure contact with an object to be charged by a means. Claim 2: The oscillating voltage is 2 times higher than the charging start voltage of the charged object.
A contact charging device characterized in that the voltage is a superimposed voltage of an AC voltage having a peak-to-peak voltage that is more than double that of a DC voltage. 3. The contact charging device according to claim 1, wherein the blade-shaped charging member also serves as a cleaning blade for the charged object.