JPH06202433A - Contact elecrifying device - Google Patents

Abstract

PURPOSE:To accurately form electrifying width having uniform potential on a photosensitive drum and to prevent faulty elecrification. CONSTITUTION:An electrifying roller 15 is brought into contact with the photosensitive drum 7, so that a contact nip part N is formed between them. By driving and rotating the drum 7, and making the roller 15 plate following it, then voltage is impressed on the roller 15 to electrify the drum 7. Insulating members 2 which are annular and have an insulating surface 2a crossing with the contact nip part N are arranged at both ends of the roller 15. Thus, the electrifying width L having the uniform potential is accurately formed on the drum 7.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging device which is mounted on an image forming apparatus such as a laser beam printer of a copying machine to charge an image carrier as a member to be charged. , Contact the charging member to which voltage is applied,
The present invention relates to a contact charging device that charges the image carrier uniformly.

[0002]

2. Description of the Related Art Conventionally, a corona charger has been widely used as a charging processing means for charging an object to be charged such as a photosensitive drum.

The corona charger is effective as a means for uniformly and evenly charging the surface of the body to be charged to a predetermined potential, but on the other hand, it requires a high voltage and therefore requires a high voltage power source. There is also a problem that undesired ozone is generated on the body to be charged and the human body during discharge.

With respect to such a corona charger, a contact type charging device for charging the surface of the body to be charged by bringing a conductive charging member to which a voltage is applied into contact with the surface of the body to be charged, a so-called contact charging device Has advantages such as lowering the voltage of the power source and the amount of ozone generated, and has been put into practical use in recent years.

By the way, after uniformly charging the charged body, imagewise exposure is performed on the charged body to form an electrostatic latent image on the image carrier, and the latent image is developed by a developing device to form an image. Although it is visualized as a toner image on the carrier, this developing method is roughly classified into two methods.

First, as one method, a method called normal development, which has been widely used in analog type copying machines, is used. Toner is adhered to a region having a high charge potential after image exposure and a toner is applied to a region having a low charge potential. This is a method in which toner is not attached.

Another method is a method called reversal development, which is often used in a part of a digital copying machine or an LBP (laser beam printer), in which toner is attached to a region having a low charging potential after image exposure. This is a method in which toner is not attached to high areas (this latent image forming method is called image scanning by lowering the potential by exposing areas corresponding to the image).

In both the regular development and the reversal development described above, the width of the transfer material in the left-right direction with respect to the advancing direction is not less than the required image width, and the developing width is not less than that. I have to. Therefore, charging width ≧
The relationship of development width ≧ image width is satisfied.

Now, considering the area of (development width-image width), in the case of regular development, if this area is charged, development with toner is performed, which is inconvenient. On the other hand, in the case of reversal development, even if this area is charged, the toner is not developed, so there is no particular inconvenience. On the contrary, if the area (development width-image width) is not charged, development by toner is not possible. It will be inconvenient because it is done.

Therefore, in reversal development, it is possible to prevent toner adhesion in an unnecessary (development width-image width) area by allowing the charging width to be sufficiently wider than the development width. This is the same regardless of whether the charging method is corona charging or contact charging.

On the other hand, in the regular development, when the charging width is wider than the image width, unnecessary toner adheres to the area (charging width-image width), resulting in wasteful consumption of toner and flying in the apparatus. It is inconvenient. Therefore, charging width =
The image width may be used, but it is uniform in the left and right direction of the charging width (for example, the direction along the discharge wire in corona charging, and the axial direction with the other in contact charging using a charging roller), and the potential of the end portion If the image does not rise sharply without sagging, there arises such a problem that the development contrast at the end portions in the left-right direction is lowered and the image density at the end portions is lowered.

Generally, when a charged body is charged by using a corona charger, a gap of about several mm exists between the charger and the charged body, so that the potential at the left and right ends is , There is a little spread, and it is not possible to obtain a sharp rising edge of the potential.

Therefore, in the image forming apparatus for performing the normal development using the conventional corona charger, the charging area is taken to be an extra wide area in the left-right direction and the side area is exposed by the so-called side blank exposure or sharp cut. It is general to lower the potential of a part to form a charging potential having a sharp rise of the potential at the end portion with a required width on the image carrier.

On the other hand, in the case of regular development using a contact charger, for example, when blade charging is used, the contact width of the blade is sharply regulated, and the blade also comes into contact at the left and right ends. It is clear whether or not there is a potential, so the potential is obtained in the contacting part, the potential is not obtained in the non-contacting part, and the left and right ends have a sharp potential rise. It is possible to obtain a potential. In this respect, there is a merit that it is possible to form a charging potential having a sharp edge potential rise of a necessary width without providing an exposure means such as side blank exposure and sharp cut when using a corona charger. .

[0015]

However, according to the above-mentioned conventional technique, the brush charging having a spread at the end portions in the left-right direction and the roller charging having the spelled diameter at the roller end portions in the left-right direction are charged. At the end portions in the left-right direction of the portion, an unstable potential portion is generated, and a charging width having a sharp rising edge cannot be formed.

FIG. 6 shows an example thereof. The figure shows a cross section of the charging roller 1 taken along the axial direction thereof.
Is provided with a conductive inner layer 5, and an outer layer 6 having a medium resistance is further provided thereon. If the conductive inner layer 5 is largely exposed on the end surface of the charging roller 1, the applied voltage may leak. Therefore, the outer diameter is reduced at the end to prevent the leak. The potential distribution when this charging roller 1 is used is shown in FIG. In FIG. 7, a constant uniform potential is obtained in the region up to L1.
The region L2 has a low potential or an unstable potential region.

Therefore, when these contact charging devices are used in an image forming apparatus for performing regular development, it is necessary to perform side blank exposure or sharp cut exposure as in the case of using a corona charger. It was

Therefore, it is an object of the present invention to provide a contact charging device in which insulating members are arranged at both ends of a charging member so that a member to be charged can be favorably charged.

[0019]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and forms a strip-shaped contact nip portion in contact with an object to be charged, and the contact nip portion is used to form the contact nip portion. In a contact charging device that has a charging member that charges a charging body and that is mounted in an image forming apparatus that performs regular development, the contact charging device is formed in an annular shape at both ends of the charging member along the outer peripheral surface of the charging member. An insulating member having an insulating surface that intersects the contact nip portion is provided.

Further, a belt-shaped contact nip portion is formed in contact with the member to be charged and has a charging member for charging the member to be charged through the contact nip portion, and is attached to an image forming apparatus for performing normal development. In the contact charging device, a tape-shaped insulating strip that intersects the contact nip portion is provided at both end portions of the contact nip portion, and both end portions of the member to be charged and both end portions of the charging member are It is characterized in that they are brought into contact with each other through the insulating band.

[0021]

According to the above construction, the insulating surfaces are always held at both ends of the contact nip portion, and the member to be charged and the charging member are always in contact with each other through the insulating surfaces at both ends. In the contact nip portion other than the insulating surface sandwiched between the insulating surfaces, the charging member uniformly charges the body to be charged.

[0022]

Embodiments of the present invention will be described below with reference to the drawings. <Embodiment 1> First, FIG. 9 schematically shows an image forming apparatus equipped with a contact charging device according to the present invention.

This image forming apparatus has a photosensitive drum 7 as a member to be charged (image carrier). Photosensitive drum 7
Is formed by laminating an OPC photosensitive layer 7a having a thickness of 25 μm and a dielectric constant of about 3 on the surface of a conductive drum substrate 7b made of aluminum, for example, and is rotationally driven in the direction of arrow R7 at a predetermined process speed. As the image carrier,
It is not limited to the drum type described above, but may be a rotating belt type or the like. In both cases, the surface is seamless,
Not only the so-called seamless type but also the seamed type can be used by performing the respective copying steps by obtaining a synchronizing signal.

In FIG. 9, 16 is a short focus lens array which is a part of exposure means for forming a latent image on the photosensitive drum 7, 17 is a developing device, 19 is a transfer roller as transfer means, and 20 is not. The transfer material P conveyed one by one from the illustrated paper feeding section is synchronized with the rotation of the photosensitive drum 7 and is transferred to the photosensitive drum 7.
Between the transfer roller 19 and the transfer roller 19 (transfer portion), a timing roller (registration roller) 21 is provided between the timing roller 20 and the transfer roller 19, and is a transfer guide for guiding the transfer material P. .

Reference numeral 22 denotes a conveying portion for introducing the transfer material P, which has undergone the image transfer, between the photosensitive drum 7 and the transfer roller 19 to a fixing device (not shown), and 23 denotes a residual portion on the photosensitive drum 7 after the image transfer. A cleaning device for removing toner and the like, 23a is a cleaning blade, and 15 is a charging roller as a charging member that contacts the photosensitive drum 7 after cleaning to uniformly charge the photosensitive drum 7. In this embodiment, the charging roller 15 uniformly charges the photosensitive drum 7 in a negative polarity, then exposes the image, and normally develops the positively charged toner.

The image forming apparatus of the present embodiment includes the photosensitive drum 7,
Developing device 17, cleaning device 23, charging roller 15
The four process devices are collectively assembled as a process cartridge 25 having a predetermined positional relationship with each other. The process cartridge 25 is shown in the drawing along a support rail (not shown) in the main body of the image forming apparatus. Can be inserted and installed in the vertical direction,
On the contrary, it can be freely removed from the device body. By fully inserting and mounting the process cartridge 25 in the apparatus main body, the apparatus main body side and the process cartridge 25 side are mechanically and electrically coupled to each other, and the image forming apparatus becomes operable.

The charging roller 15 is a metal cored bar to which conductive rubber is adhered, and a charging voltage is applied to the cored bar 3 by a power supply 9.

FIG. 1 shows a cross section of the charging roller 15 in a direction along the core metal 3 (axis) (however, the drawing shows the charging roller 1).
5 shows only a cross section of one end of No. 5).

In the figure, reference numeral 2 denotes an insulating elastic body (insulating member) which is formed in a cylindrical shape and has an insulating surface 2a on its outer peripheral surface, and which is adhered to both end surfaces of the charging roller 15 in the longitudinal direction (axial direction). ing. A cored bar 3 is arranged in the center of the charging roller 15, an inner layer 5 which is a conductive layer is provided around the cored bar 3, and an outer layer 6 which is a medium resistance layer is laminated around the inner layer 5 to form a two-layer coating as a whole. It is composed. However, there are cases where two or more layers are provided, and cases where only one layer is provided.

FIG. 2 is a schematic perspective view showing a state where the charging roller 15 shown in FIG. 1 is in contact with the photosensitive drum 7. In the figure, the photosensitive drum 7 is rotationally driven in the direction of arrow R7 at a predetermined speed. The charging roller 15 is pressed against the surface of the photosensitive drum 7 with a predetermined pressure, forms a belt-shaped contact nip portion N between the charging roller 15 and the photosensitive drum 7, and is indicated by an arrow as the photosensitive drum 7 rotates. It rotates in the direction of R15. Of course, the charging roller 15 may be driven. 9 is this charging roller 15
To a power source for applying a superimposed ripple voltage (V _DC + V _AC) AC voltage V _AC having a peak voltage V _PP to a DC voltage V _DC. In the above-described configuration, the charging width L by the charging roller 15 is the length of the contact nip portion N between the charging roller 6 and the photosensitive drum 7, excluding the width of the insulating elastic body 2 at the left and right ends of the charging roller 15. That is, that is, the portions sandwiched by the insulating elastic bodies 2 at the left and right ends.

FIG. 8 is a diagram showing the relationship between the length of the charging roller 15 in the longitudinal direction and the surface potential. It has been experimentally confirmed that the surface potential drops to 0 V within 0.3 mm from the longitudinal end portion of the charging roller 15, and the insulating elastic body 2 of the present embodiment is used for determining the charging width L. It was confirmed that it showed excellent characteristics.

In the charging roller 15 of this embodiment, by providing the insulating elastic body 2 at both ends of the charging roller 15, it is possible to prevent the inner layer 5 which is a conductive layer from being exposed from the end surface of the charging roller 15. There is also a merit of preventing voltage leakage from the exposed portion of the inner layer 5 of the charging roller 15.

As described above, by disposing the insulating portions 2 at both ends of the charging roller 15, it becomes possible to form a charging width L having a sharp potential rise at the ends on the photosensitive drum 7. , The photosensitive drum 7 without the side blank exposure and the sharp cut provided in the image forming apparatus.
In addition, it is possible to form an effective charging width L that can prevent unnecessary adhesion of toner during development. <Embodiment 2> FIG. 3 shows a plastic insulating cap 1 at both longitudinal ends of a contact charging roller as a charging member.
It is sectional drawing at the time of providing 0. The insulating cap 10 is adhered to the outer layer 6 of the charging roller 15. According to the figure, the insulating part and the charged part have different diameters, but the cap is configured to have a difference (thickness) between the outer diameter and the inner diameter of 300 μm or less in consideration of durability and insulation. Since the charging roller 15 itself is an elastic body,
The insulating portion and the charging portion of the charging roller 15 can be in contact with each other on the photosensitive drum.

When the above-mentioned charging roller 15 is used, the insulating cap 10 can be easily attached and mass production is possible at low cost, which is a great cost advantage. <Embodiment 3> FIG. 4 shows a charging roller 15 as a charging member.
FIG. 6 is a cross-sectional view in the case where both ends in the longitudinal direction are coated with an insulator. Reference numeral 11 indicates the coated insulator. According to FIG. 4, the insulating part and the charged part have different diameters, but the coating is set to 150 μm or less in consideration of durability, and both the charged part and the insulating part of the charging roller 15 are elastic. Since the charging roller 15 is a body and also contacts the photosensitive drum 7 with a predetermined pressure, both the charging portion and the insulating portion contact the photosensitive drum.

When the above charging roller is used, since the insulating portion is coated, the bonding step is unnecessary, and it does not have to be composed of a plurality of parts. Therefore, the manufacturing cost can be kept low. <Embodiment 4> FIG. 5 is a schematic configuration diagram in the case where a tape-shaped insulating sheet (insulating band) is provided between the photosensitive drum 7 and the longitudinal end of the charging roller 15.

The insulating sheets 12 respectively arranged at both ends of the charging roller 15 are unwound from the roller 13a and cross at both ends of the contact nip portion N, and then the roller 1
It is wound up by 3b. In addition, since the insulating sheet is designed to have a thickness of 300 μm or less in consideration of durability and insulating properties, both the charged portion and the insulated portion of the charging roller 15 are in contact with the photosensitive drum 7.

When the charging roller 15 is used, the insulating sheet 12 has an advantage that both ends of the photosensitive drum 7 are cleaned at the same time when the charging width is determined. The charge width will not be blurred due to dirt or other reasons.

Further, since the insulating sheet 12 of this embodiment is formed in a tape shape and new ones can be sequentially supplied, the insulating members of the above-mentioned first to third embodiments are used for a long time. It is possible to always achieve a constant withstand pressure, unlike the case where the withstand pressure causes insufficient withstand pressure.

As described above, also in the second to fourth embodiments, as shown in FIG. 8, the sharp rise of the potential as in the first embodiment can be realized. Further, since the image width is determined only by the position of the charging member in all the embodiments, when the charging member and the photosensitive drum 7 are integrated into a process cartridge structure, the conventional image forming apparatus is used. There is also an advantage that the image width can be regulated more accurately because there is no backlash between the apparatus body and the process cartridge, compared to the regulation of the image width formed by side blank exposure and sharp cut provided on the body.

Further, in the above embodiments, the charging roller 15 was used as an example of the charging member, but the present invention is not limited to this. For example, a brush that is likely to cause potential unevenness or sagging at the end portion. It can be applied to all other contact charging devices such as a charging device and a charging blade made of a plate-shaped elastic body.

[0041]

As described above, according to the present invention,
By providing insulating members at both ends of the contact nip portion between the member to be charged and the charging member, it has been conventionally provided in the image forming apparatus main body in regular development in order to improve the accuracy of determining the charging width. It is not necessary to provide side blank exposure and sharp cut, which are required, and it is possible to form a good charge width with a simple configuration, and therefore it is possible to perform image formation with excellent image quality without blurring. .

[Brief description of drawings]

FIG. 1 is a longitudinal cross-sectional view of one end of a charging roller according to a first exemplary embodiment.

FIG. 2 is a perspective view illustrating the operation of the charging roller according to the first exemplary embodiment.

FIG. 3 is a longitudinal cross-sectional view of one end of a charging roller according to a second exemplary embodiment.

FIG. 4 is a longitudinal cross-sectional view of one end of a charging roller according to a third exemplary embodiment.

FIG. 5 is an operation explanatory view of the contact charging device of the fourth embodiment.

FIG. 6 is a longitudinal sectional view of one end of a conventional charging roller.

FIG. 7 is a diagram showing a conventional relationship between the length of the charging roller in the longitudinal direction and the surface potential of the photosensitive drum.

FIG. 8 is a diagram showing the relationship between the length of the charging roller in the longitudinal direction and the surface potential of the photosensitive drum in the present invention.

FIG. 9 is a vertical cross-sectional view schematically showing an image forming apparatus equipped with the contact charging device according to the present invention.

[Explanation of symbols]

 2 Insulating member (insulating elastic body) 2a Insulating surface 7 Charged member (image bearing member, photosensitive drum) 12 Insulating band (insulating sheet) 15 Charging member (charging roller) N Contact nip part

Claims (2)

[Claims] 1. A charging member for contacting an object to be charged to form a belt-shaped contact nip portion, and charging the object to be charged through the contact nip portion, and being mounted on an image forming apparatus for performing regular development. In the contact charging device, an insulating member is formed at both ends of the charging member, the insulating member having an insulating surface formed in an annular shape along the outer peripheral surface of the charging member and intersecting the contact nip portion. A contact charging device characterized in that 2. A charging member that forms a strip-shaped contact nip portion in contact with a member to be charged and charges the member to be charged through the contact nip portion, and is attached to an image forming apparatus for performing regular development. In the contact charging device, a tape-shaped insulating band that intersects the contact nip portion is provided at both end portions of the contact nip portion, and both end portions of the member to be charged and both end portions of the charging member are A contact charging device, wherein each contact is made via the insulating band.