JP2892071B2 - Charging device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging device for charging a surface of an object to be charged to a predetermined polarity.

[Conventional technology]

For example, a photoconductor used in an image forming apparatus such as an electronic copying machine, a printer, or a facsimile is charged to a predetermined polarity prior to exposure in order to form an electrostatic latent image on the surface thereof.

Conventionally, a corona discharger that applies a voltage to a charge wire to generate a corona discharge has been widely used to charge such an object to be charged. However, when a corona discharger is used, it is necessary to apply a high voltage to the charge wire, so that a large amount of ozone is generated during discharge.

Therefore, a semiconductive resistor blade is brought into contact with the surface of the photoreceptor, a DC voltage is applied to the blade, a charge is injected into the photoreceptor by a leak current to the photoreceptor, and this is charged. A device has been proposed. However, according to this charging device, the charging operation by charge injection is performed while the blade is in direct contact with the surface of the photoreceptor while the two are relatively moved, so that a stripe-shaped charging unevenness occurs on the surface of the photoreceptor. If such unevenness occurs, streaks are formed on the image after development, which causes deterioration in image quality.

There has also been proposed a charging device in which a charging roller formed by laminating a resistor around a conductor is brought into contact with the photoconductor, and the photoconductor is charged by a voltage applied to the conductor. Since the rollers need to be driven to rotate, the structure of the apparatus becomes complicated and the cost increases.

Furthermore, a charging device is proposed in which a direct current voltage is applied to a charging member, which is provided in proximity to the surface of the photoconductor and is made of a conductor coated with a resistor on the surface to generate a discharge, thereby charging the surface of the photoconductor. (See JP-A-58-76851). According to this configuration, the charging member is separated from the photoconductor, and there is no need to rotationally drive the charging member. Therefore, the drawbacks seen in the above two conventional examples do not occur. However, the surface of the photoreceptor has undulations, albeit slightly, and its peripheral surface is often eccentric. When such a photosensitive member is used, the distance between the moving photosensitive member surface and the charging member constantly changes. The size of the interval greatly affects the discharge, and the variation in the interval causes the charge amount on the surface of the photoconductor to become non-uniform, which may deteriorate the image quality of the image. [Problems to be Solved by the Invention] An object of the present invention is to provide a charging device in which the above-mentioned conventional disadvantages are eliminated by a simple configuration.

[Means for solving the problem]

In order to achieve the above object, the present invention has a charging blade having a tip portion abutting on a member to be charged, and arranged so as to form a wedge-shaped gap between the member and the member to be charged. A charging device having a resistor as a discharge electrode to which a voltage is applied to a portion facing the member to be charged, wherein the resistor is located in a non-contact state with the member to be charged. We propose (Claim 1).

At that time, the charged part blade portion in contact with the member to be charged,
It is advantageous that the member to be charged is made of a material that does not cause frictional charging (claim 2).

Further, in the charging device according to claim 1, the charging blade portion in contact with the member to be charged is made of a material that frictionally charges the member to be charged to the same polarity as the charging polarity of the member to be charged due to discharge from the resistor. It is advantageous if it is configured (claim 3).

〔Example〕

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

FIG. 1 shows an example of an electronic copying machine using a charging device according to one embodiment of the present invention. First, the overall configuration will be briefly described.

A photosensitive member 1 formed in a drum shape has a cylindrical conductive substrate 2 and a photosensitive layer 3 laminated on the surface thereof, and is driven to rotate clockwise in the drawing. At this time, the surface is uniformly charged to a predetermined polarity by a charging device 4 described in detail later, and the charged photoreceptor surface is exposed to an image in an exposure unit 5. Thus, an electrostatic latent image is formed on the surface of the photoconductor, and this latent image is formed into a toner image by the developing device 6. This toner image is transferred to the transfer paper 7, and the toner remaining on the surface of the photoconductor after the transfer is cleaned by the cleaning device 20, and then the surface of the photoconductor is subjected to a charge removing operation by the charge removing device including the charge removing lamp 8.

The charging device 4 has a charging blade 9 as shown in an enlarged manner in FIG. 2, and the tip of the blade 9 is opposed to the moving direction of the photoreceptor 1 constituting an example of the member to be charged.
It is arranged so as to abut on the surface of the photoconductor 1 and form a wedge-shaped gap 10 between the photoconductor 1 and an example of the member to be charged. That is, the charging blade 9 is positioned in a so-called counter direction with respect to the photoconductor 1, and the tip portion thereof is
In contact with the surface.

The charging blade 9 illustrated in FIGS. 1 and 2 has a blade substrate 11 made of an elastic plate, the base end of which is a holder.
The blade 12 is fixed to the machine frame of the copier body via the front end 12, and the leading end thereof is pressed against the surface of the photosensitive member 1 by the elasticity of the blade substrate itself.

The charging blade portion facing the surface of the photoreceptor 1 with a wedge-shaped gap 10 therebetween is provided with a lead electrode 14 made of a layered conductor connected to a power supply 13 and a resistance as a discharge electrode covering the whole. The electrophysiological device 15 is provided integrally, and the resistor 15 is not in contact with the photoconductor 1.

As described above, the photoreceptor 1 rotates clockwise in FIG. 1 and passes through the tip portion of the blade substrate 11 in contact with its surface. At this time, a voltage obtained by superimposing an alternating current on a direct current is applied by the power supply 13 between the lead electrode 14 and the conductive base 2 of the photoreceptor 1 which is a counter electrode thereof. Thus the resistor
Since a voltage is applied to the photoconductor 15, a corona discharge occurs between the resistor 15 and the photoconductor 1, and the surface of the photoconductor 1 is uniformly charged to a predetermined polarity (in this example, negative polarity). The fact that the surface of the photoreceptor is charged by corona discharge is apparent from the fact that a light emission (discharge) phenomenon is observed in the gap 10 by an experiment in the dark. As described above, the charging blade 9 has the resistor 15 as a discharge electrode to which a voltage is applied at a portion facing the member to be charged made of the photoconductor 1, and the resistor 15 is in contact with the member to be charged. It is located in contact.

In the charging device 4 shown in FIGS. 1 and 2, charge is not injected by a resistor blade contacting the photoreceptor 1, but the surface of the photoreceptor is charged by corona discharge. The problem that streak-like uneven charging occurs on the surface of the photoconductor can be suppressed. The starting voltage of this discharge is usually about several hundred volts, and the applied voltage can be greatly reduced as compared with a conventional corona discharger in which a voltage of several thousand volts is applied to a charge wire to demagnetize corona discharge. For this reason, the generation amount of ozone can be effectively suppressed, and deterioration of the photoconductor can be suppressed.

Also, unlike conventional charging devices that use a charging roller,
Since it is not necessary to drive the charging blade, the structure of the apparatus can be simplified, and the cost can be reduced.

Furthermore, even if the surface of the photoconductor 1 has undulating irregularities or the photoconductor itself is eccentric, the blade substrate 11 that contacts the surface of the photoconductor 1 elastically deforms in accordance with the unevenness and the eccentricity. Since it follows the surface of the photoreceptor, the size of the gap 10 between the resistor 15 and the surface of the photoreceptor 1 is always constant.
For this reason, unlike a conventional charging device in which the charging member is disposed apart from the photoconductor, a problem that the charge amount on the photoconductor surface becomes non-uniform can be suppressed, and a high-quality image (toner image) can be obtained. .

As described above, the resistor 15 serves as a discharge electrode to which a voltage is applied, and is made of a material capable of achieving this function. At this time, assuming that the resistor 15 contacts the photoconductor 1, it is necessary to select a constituent material of the resistor so that the contact does not adversely affect the charging of the photoconductor 1. There is. That is, when the resistor 15 is brought into contact with the photoconductor 1, the resistor 15
As a material constituting 15, it is necessary to select a material which can achieve the original purpose of the discharge electrode and which does not impair the electrocardiographic property of the photoreceptor 1, and there is room for selection of the material. .

On the other hand, as in the embodiment shown in FIG.
If the resistor 15 is configured not to be in contact with the photoconductor 1, the resistor 15 can be formed of a material that can achieve the purpose of the discharge electrode exclusively without considering the influence of the contact between the resistor 15 and the photoconductor 1. Since it can be configured, the room for selecting the material of the resistor 15 can be expanded.

In the charging device 4 shown in FIGS. 1 and 2, the tip of the charging blade 9 is in contact with the photosensitive member 1 in the moving direction, so that the leading end of the charging blade 9 contacts the photosensitive member 1.
The cleaning function can be performed, and toner and other dust can be prevented from entering the gap 10 where corona discharge is performed, and a stable discharge can be generated.

The position of the charging blade 9 may be reversed in the trailing direction with respect to the photoreceptor 1 with respect to the case of FIGS. 1 and 2, but in this case, dust enters the gap between them. As a result, the corona discharge becomes uneven. As a result, not only is the unevenness of the charged position on the photoreceptor surface, but also dust passes between the charging blade and the photoreceptor, and at this time, the blade moves in a direction away from the photoreceptor, and the discharge gap fluctuates.
This also inevitably causes uneven charging. Further, since the charging blade itself has a cleaning function for the photoconductor 1 as described above, the cleaning device 20 shown in FIG. 1 is eliminated, and the toner remaining on the photoconductor surface after transferring the toner image is charged. It is also possible to adopt a configuration in which cleaning is performed only with the blade.

In addition, the tip of the charging blade 9, in the example shown in FIG. 2, the tip of the blade substrate 11 is in contact with the surface of the photoreceptor 1. Even if it is charged, it is desirable to select the material of the blade substrate 11 so as to be charged by corona discharge of the resistor 15 (corresponding to frictional charging to the negative polarity 9. The surface of the photoreceptor is largely frictionally charged to the positive polarity side by the charging blade 9. When the photoreceptor is charged negatively by corona discharge, uneven charging occurs on the surface of the photoreceptor, which may cause density unevenness in an image, provided that the amount of charge due to frictional charging is positive. Even if there is little, or if frictional charging is performed in the same polarity as the charging polarity by corona discharge, this frictional charging can be corrected by corona discharge by the resistor 15 and the charging device It can be uniformly charged to a predetermined negative polarity of the photosensitive member surface after passing through the.

As described above, the charging blade portion in contact with the member to be charged composed of the photoreceptor 1 is made of a material that does not frictionally charge the member to be charged, or the charging blade portion in contact with the member to be charged However, it is desirable that the charging member be made of a material that frictionally charges the member to be charged to the same polarity as the charging polarity of the member to be charged by the discharge from the resistor 15.

As described above, in the embodiment shown in FIG. 2, the material of the blade substrate 11 must be selected in consideration of the triboelectric series on the surface of the photoconductor, and the blade substrate 11 may be damaged or worn by contact with the photoconductor 1. It is necessary to select a material with good lubricity that does not easily cause cracks. Further, the tip portion is in close contact with the surface of the photoreceptor so that toner and dust do not pass between the tip portion of the blade substrate 11 and the photoreceptor 1 and automatically responds to undulation and eccentricity of the photoreceptor surface. Gap 10 where corona discharge occurs
It is desirable that the blade substrate 11 be made of a material having elasticity that can always keep the distance between the blade substrates 11 constant. As a material of such a blade substrate 11, for example, a polyurethane rubber or a plate made of a thin metal or resin can be used. At this time, if the material is a conductive material such as a metal, the leading end of the blade substrate 11 is coated with an insulator to prevent the lead electrode 14 and the photosensitive member 1 from being in a conductive state. There is a need to.

Since the resistor 15 generates a corona discharge in a minute gap between the resistor 15 and the photoconductor surface, a predetermined current flows,
Also, it is desirable to use a resistor that does not burn the photosensitive layer 3 by spark discharge even when a small amount of dust passes between the charging blade 9 and the photosensitive member 1. Others
The resistance value of the resistor 15 should be determined in consideration of the copy speed, the gap space where corona discharge occurs, the capacitance of the photoreceptor 1, its charging potential, applied voltage, its waveform, and the like. Is usually set to about 10 ^{4 to} 10 ¹⁰ Ω · cm. Furthermore, when discharging, it is inevitable that a small amount of ozone that cannot be detected is inevitably generated.
For 15, it is desirable to select a material that is oxidation resistant and has excellent durability against spatter.

The voltage applied to the resistor 15 may be DC only, but when a voltage obtained by superimposing AC on DC is applied by the power supply 13 as in this example, corona discharge is stabilized, and the surface of the photoconductor is made more uniform. To be charged.

Incidentally, corona discharge generated between the resistor 15 and the photoconductor 1 is easily affected by environmental changes due to humidity and the like. For example, when the humidity increases, the discharge becomes difficult, and when the humidity decreases, the discharge easily occurs. Although the tip of the charging blade 9 which is in contact with the photoreceptor 1 is made of a material which does not easily wear, if used over a long period of time, some wear is inevitable. However, when such abrasion occurs, the distance between the discharge gaps changes, whereby the current flowing through the lead electrode 14 changes, and the charging potential of the photoconductor 1 may change.

From such a viewpoint, in the charging device 4 shown in FIG. 2, the constant current control device including the detection resistor and the capacitor is used.
21 is provided to control the current flowing through the lead electrode 14 to be always constant, even if the environment changes or the discharge gap changes due to wear of the leading end of the charging blade 9, so that the surface of the photoreceptor can be controlled. It is configured so that the charging potential can be kept constant. Such a constant current control device 21 removes the charge of the surface of the photosensitive member 1 by a charge removing device such as a charge removing lamp 8 shown in FIG. It is desirable to employ this method when the surface of the photoconductor is not or is not triboelectrically charged at the tip. It is also possible to charge the surface of the photoreceptor after transfer of the toner image to a predetermined polarity simply by charging the surface of the photoreceptor with a charging device without providing a charge removing device. When the surface of the photoreceptor is frictionally charged to a relatively large negative polarity, the constant current control device 21 is abolished and the lead electrode 14 is controlled at a constant voltage, thereby causing a change in the environment or a change in the discharge gap. Also, the surface of the photoconductor can be uniformly charged.

In the experiment, a polyurethane-based rubber having a high toner removing effect and excellent abrasion resistance was used as the blade substrate 11, one side of which was coated with a lead electrode 14 in a layered form, and a volume specific resistivity 10 ⁷ A charging blade 9 was used in which a resistor 15 made of a resin of about Ω · cm was coated in a layer.
In order to prevent spark discharge during the charging operation, the entire lead electrode 14 was covered with a resistor 15, and a distance d according to the resistance value of the resistor 15 was taken between both ends of the lead electrode 14 and the resistor 15. (FIG. 2). Such a charging blade 9 is incorporated in a copying machine (KR type OPC) manufactured by Ricoh Co., Ltd., and a DC power source 90 between the conductive substrate 2 of the photoreceptor 1 and the lead electrode 14 is used.
When a voltage superimposed on _two sine waves of 0 V and 1 KH AC was applied, the photoreceptor surface was uniformly charged to about -450 volts. When the edge portion of the blade substrate 11 in contact with the photoreceptor surface makes about 100,000 copies,
Although it was worn by about 40 to 60 μm, the provision of the constant electrode control device 21 ensured a stable charging operation.

By the way, as described in the section of the prior art, the conventional charging roller formed by laminating a resistor around a conductor performs a charging operation by contacting the surface of the photoconductor. If there is a minute hole (pinhole) in the photosensitive layer of the body, the conductive substrate thereunder is exposed, and this portion comes into direct contact with the resistor of the charging roller. In this case, a spark discharge is generated between the resistor of the charging roller and the conductive base of the photoconductor, and the pinholes of the photoconductor layer are further increased, which may shorten the life of the photoconductor. In order to prevent this problem, the resistance of the resistor of the charging roller may be increased, but in this case, charging efficiency is reduced.
In order to charge the surface of the photoreceptor to a predetermined potential, the rotation speed of the photoreceptor must be reduced, and the copy speed is reduced.

However, in the charging device shown in FIGS. 1 and 2, since the resistor 15 is separated from the photoconductor 1 and generates a corona discharge between the two, even if there is a pinhole in the photoconductive layer 3 of the photoconductor 1, No spark discharge occurs. Therefore, the photoconductor 1 can be rotated at a high speed.

As described above, in the example of FIG. 2, the occurrence of spark discharge is prevented by separating the resistor 15 from the photoconductor 1, but as shown in FIG. If the distance d to the tip is sufficiently larger than the thickness t of the resistor 15, even if the tip of the resistor 15 is brought into contact with the photoreceptor 1, the above-described spark discharge due to the pinhole of the photosensitive layer 3 will not occur. Can be prevented. That is, by setting the distance d large as described above, the resistance value from the tip of the lead electrode 14 to the tip of the resistor 15 increases, so that even if the tip is in contact with the photoreceptor 1, The spark discharge by the hole can be prevented. On the other hand, the corona discharge for charging the photoreceptor 1 occurs in the small gap portion between the photoreceptor 1 and the resistor 15 as indicated by the symbol X in FIG. 3, and therefore does not hinder the corona discharge.

In the example shown in FIG. 3, the resistor 15 is formed up to the leading edge of the blade substrate 11, and after assembling it as shown in FIG.
Is rotated, and the tip of the resistor 15 is scraped off by friction with the photoreceptor 1 to thereby remove the resistor as shown in FIG.
The tip of 15 is brought into smooth contact with the surface of the photoconductor 1.

In the embodiment shown in FIG. 4, the charging blade 9 is pivotally connected to the machine frame of the copying machine via a pin 22 so as to be rotatable in the direction of the arrow, and the tip of the blade 9 is moved by the tension spring 23 to the surface of the photosensitive member 1. Is pressed against. According to this configuration, even if the charging blade 9 is formed of a rigid body, the blade 9 can be swung in accordance with the undulation or unevenness of the photoreceptor surface, and the discharge gap can be kept constant.

In the embodiment shown in FIG. 5, the blade substrate 11 is made of a conductor such as a metal plate, and the resistor 15 is directly formed on the conductor. The blade substrate 11 also serves as the lead electrode 14. In this case, as described above, an insulating material 11 such as resin or rubber having excellent sliding characteristics is attached to the tip of the blade substrate 11.
a is attached, and this is brought into contact with the photoreceptor surface.

In the embodiment shown in FIG. 6, the charging blade 9 is joined to the lower surface of the pressing member 31 which is slidably guided in the direction approaching or separating from the photoconductor 1 by the guide member 30, and the pressing member 31 is connected. The distal end portion of the charging blade 9 is brought into contact with the photoconductor 1 by applying pressure toward the photoconductor 1 by the compression spring 32.

In the embodiment shown in FIG. 7, the tip end surface 11b of the blade substrate 11 faces the surface of the photoreceptor 1, and the tip end portion 11c faces the surface of the photoreceptor 1 in the rotation direction of the photoreceptor 1. Abut. A wedge-shaped space 10 is formed between the tip surface 11b and the photoconductor 1, and a resistor 15 covering the lead electrode 14 is integrally formed on the tip surface 11b. The charging blade 9 thus configured is spring-biased in the direction indicated by the arrow P or Q, and the leading end portion 11c is pressed against the photosensitive member 1. According to this embodiment, there is obtained an advantage that the installation space for the charging blade 9 can be reduced.

Another configuration of the embodiment shown in FIG. 4 to FIG.
Obviously, the configuration can be the same as that shown in FIGS.

Although the specific example in which the member to be charged is a photoreceptor has been described above, the present invention can be widely applied to other members to be charged, for example, when charging a derivative belt that conveys a sheet such as copy paper. It is.

〔The invention's effect〕

According to the charging device of the first aspect, the amount of ozone generated can be suppressed, uneven charging on the surface to be charged can be prevented, the structure can be simplified, the cost can be reduced, and the material constituting the resistor can be reduced. This gives you more options.

According to the charging device of the second or third aspect, it is possible to effectively suppress the occurrence of uneven charging of the member to be charged.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an example of an electronic copying machine using a charging device according to an embodiment of the present invention, FIG. 2 is an enlarged sectional view of the charging device shown in FIG. 1, and FIGS. The figure is a diagram showing another example of the charging device. 4 Charging device 9 Charging blade, 10 Gap, 15 Resistor

Claims (3)

(57) [Claims] A charging blade disposed at a leading end of the charging blade so as to abut on the member to be charged and to form a wedge-shaped gap with the member to be charged; A charging device having a resistor serving as a discharge electrode to which a voltage is applied, the resistor being located in a non-contact state with the member to be charged. 2. A charging blade portion in contact with a member to be charged,
The charging device according to claim 1, wherein the charging device is made of a material that does not frictionally charge the member to be charged. 3. A charging blade portion in contact with an object to be charged,
The charging device according to claim 1, wherein the charging device is made of a material that frictionally charges the charged body to have the same polarity as the charged polarity of the charged body due to discharge from the resistor.