JP2735046B2 - Charging device for image forming apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for charging an electrostatic latent image carrier of a printer or a facsimile using an electrophotographic process, and more particularly to a charging device for the same.

[0002]

2. Description of the Related Art A scorotron using a corona discharge from a wire electrode is generally used for charging an electrostatic latent image carrier in an image forming apparatus using a conventional electrophotographic process. However, the scorotron must apply a high voltage of several KV to the electrodes for corona discharge, which increases the cost of the high-voltage power supply, and the ozone generated by the discharge adversely affects the human body and the environment. There are problems such as damage to the latent image carrier and the rollers around it. In order to improve these, a charging device in the form of a rotating roller or a brush which comes into contact with the electrostatic latent image carrier is provided. One that charges a carrier has been implemented. These contact charging means include a roller-shaped roller having metal oxide or carbon powder dispersed in an EPDM rubber roller and having semi-conductivity, and a brush-shaped member having carbon dispersed in fibers such as rayon and having semi-conductivity. There is something.

[0003]

The image forming member using the contact charging system requires a sufficient nip width between the electrostatic latent image carrier and the charging member in order to obtain good charging characteristics. Had to increase the pressure between them. For this reason, there have been disadvantages that the surfaces of the electrostatic latent image carrier and the charging member are easily damaged, and the torque of the apparatus is increased.

In the case of a contact type charging member such as a brush or a roller, the amount of charge and the charging potential applied to the electrostatic latent image carrier depend on the resistance value of the charging member and the contact resistance between the charging member and the electrostatic latent image carrier. Although greatly dependent on the resistance value, the resistance value is easily affected by the environment such as the contact area and the temperature and humidity, and the charge potential of the charge amount greatly varies. Further, there is a problem that shaving powder and fogging toner of the electrostatic latent image carrier accumulate on a brush or a roller during printing, and the charging ability is remarkably different between the initial stage of printing and the life of the image forming member.

Further, in the case of a brush-like charging member, the brush falls down in the downstream direction of the rotating electrostatic latent image carrier,
As the number of printed pages increases, charging characteristics such as the charging potential of the electrostatic latent image carrier fluctuate. In addition, the charging by the brush, the charging of the electrostatic latent image carrier at the tip or antinode of each brush, the charging unevenness like sweeping unevenness in the rotation direction of the electrostatic latent image carrier is likely to occur, When a halftone dot image is printed, there is a problem such as a sweeping uneven image on a line in the paper traveling direction. In addition, abnormal discharge is likely to occur because the brush bristles are in contact with the electrostatic latent image carrier, and the frequency of occurrence of damage to the electrostatic latent image carrier and pinholes due to white spot images and overcurrent is high. It was big.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and has been made in view of the above-mentioned circumstances.
A charging device that applies electric charge to the surface of an electrostatic latent image carrier by applying a bias voltage to charge the surface of the image bearing member has an elastic roller that is driven to rotate, and has a peripheral length longer than the peripheral length of the elastic roller. It has a sleeve-like seamless thin film member provided outside the roller.

Further, in addition to the above configuration, the elastic roller is in contact with the electrostatic roller via a seamless thin film member, and a space is provided between the elastic roller and the seamless thin film member at a portion facing the electrostatic latent image carrier and the print medium. A stable space portion and a constant contact pressure of the seamless thin film member can be formed by providing a support member that forms the portion and makes the outer surface of the seamless thin film member covering the space portion adhere to the electrostatic latent image carrier. . Further, it is more effective to clean the surface of the seamless thin film member by using a member having a cleaning property for the support member.

[0008]

Next, an embodiment of the present invention will be described with reference to the drawings. First, referring to FIG.
An overall configuration of an image forming apparatus according to an embodiment of the present invention will be described.

The charging member 1 is disposed to face an electrostatic latent image carrier 2 such as a photosensitive drum, and the electrostatic latent image carrier 2 is configured to be driven to rotate clockwise in FIG. Charging member 1
Is driven to rotate in the same direction (counterclockwise) as the electrostatic latent image carrier, uniformly applies charges to the electrostatic latent image carrier, and charges the electrostatic latent image carrier to a constant potential. .

After the printing medium (paper or the like) has been charged, the paper is not fed (between papers) until the next printing medium is fed. In order to prevent the toner on the latent image carrier and the shavings of the electrostatic latent image carrier from transferring to the charging member, a bias having a polarity opposite to that of the charging is applied to the charging member 1 or the charging bias is applied only between sheets. Is turned off. This is because, in many cases, the fog toner on the electrostatic latent image carrier and the shavings of the electrostatic latent image carrier are positively charged, whereas in the present embodiment, the electrostatic latent image carrier 2 is charged to a negative polarity, and a reversal development method using a non-magnetic toner having a negative charge is used, so a negative bias is applied during charging, and a positive bias is applied during non-paper passing (between sheets). Alternatively, the charging bias is turned off so that the charging member does not transfer fog toner or shavings.

After uniformly charging the entire surface of the electrostatic latent image carrier 2 by the charging member 1, image data is exposed from a light source such as a laser (not shown) to form an electrostatic latent image.

The toner hopper 3 is arranged opposite to the electrostatic latent image carrier 2 and has a structure for storing the toner 4. The toner in the toner hopper is supplied to a toner carrier 7 which is rotated in a counterclockwise direction by a toner supply member 6 which is agitated by a stirring member 5 and driven to rotate in a counterclockwise direction. The toner carrier is made of, for example, a metal roller made of stainless steel, aluminum or the like, and an elastic material such as silicone, nitrile-butadiene copolymer, urethane rubber, etc. provided on the outer periphery thereof. The elastic portion of the toner carrier has a rubber hardness of 30 to 40 degrees according to the JIS A hardness tester in consideration of the contact pressure with the thin layer forming member and the electrostatic latent image carrier, and further has a low resistance of the toner carrier. The resistance between the roller surface and the shaft is desirably 10 ⁵ to 10 ⁶ Ω in consideration of leakage to the electrostatic latent image carrier, fog due to high resistance, and the like. The particle size of the negatively chargeable polyester-based toner used in this embodiment is about 7 to 8 μm. To uniformly charge the toner, the ten-point average surface roughness Rz of the toner carrier is 7 μm or less. It is desirable that

The toner 4 supplied to the toner carrier 7 is
It is triboelectrically charged and regulated by the thin layer forming member 8 to form a more or less uniform thin layer. The thin layer forming member 8 is made of a spring material made of a thin metal plate such as stainless steel or phosphor bronze, or a material in which silicone rubber is applied to a contact portion with a toner carrier. The charged toner in a thin layer on the toner carrier is carried to the portion where the toner carrier 7 and the electrostatic latent image carrier 2 face each other as the toner carrier 7 rotates, and the surface of the electrostatic latent image carrier 2 is An electric field based on the potential difference between the potential and the bias voltage applied to the toner carrier 7 moves to the electrostatic latent image on the surface of the electrostatic latent image carrier to form a toner image.

The toner image developed on the electrostatic latent image carrier is conveyed to a portion opposed to the transfer member 9, and is printed on a nip portion between the electrostatic latent image carrier 2 and the transfer member 9 in contact with the transfer member 9. Medium 10
, The transfer member 9 applies a voltage having a polarity opposite to that of the toner from the back of the print medium 10 to transfer the developing toner layer on the electrostatic latent image carrier side to the print medium 10. At the time of non-transfer after the transfer to the printing medium 10 is completed until the next medium passes, in order to clean the toner on the transfer member and to prevent the toner on the electrostatic latent image carrier from transferring to the transfer member 9. A bias having a polarity opposite to that of the transfer is applied to the transfer member 9. In the present embodiment, a positive bias is applied at the time of transfer and a negative bias is applied at the time of non-transfer because a non-charged non-magnetic toner is used.

Next, a charging member according to an embodiment of the present invention used in the image forming apparatus of FIG. 1 will be described with reference to the drawings. FIG. 2 is an enlarged sectional view of the charging member 1. The elastic roller 13 of the charging member 1 is formed of a metal shaft such as stainless steel or aluminum provided with a foam or rubber material such as silicone, urethane, nitrile, or ethylene-propylene copolymer provided with conductivity on the outer periphery. I have. This elastic roller is separated from the electrostatic latent image carrier 2 at an appropriate interval. Seamless thin film member 1 covered by the elastic roller
Reference numeral 2 denotes a sheet having a longer circumference than the outer circumference of the elastic roller, and is made of a sheet formed by adding carbon powder or metal oxide to a fluororesin such as polyamide or PFA or polyurethane. About 200 μm. Here, the volume resistance value of the elastic roller for obtaining good and stable charging efficiency and charging potential in response to environmental fluctuation and short circuit and damage to the electrostatic latent image carrier due to pinholes and the like is 10 ³
~10 ⁴ Ω · cm, the volume resistivity of the seamless thin film member is 10 ⁵ ~10 ⁷ Ω · cm.

As shown in FIG. 2, a part of the seamless thin film member 12 mounted on the outer periphery of the elastic roller 13 is supported by a support member 14 from the outside of the thin film member so as to be in close contact with the elastic roller 13. Examples of the support member 14 include fine polyester fibers having a cleaning property and pads having elasticity such as felt made of a binder of polyester and polyurethane. There is no support member outside the seamless thin film member 12 on the side that comes into contact with the electrostatic latent image carrier 2, and since the seamless thin film member 12 has a longer circumference than the elastic roller 13, it is supported by the support member 14. The extra length gathers at the contact portion with the electrostatic latent image carrier 2 which is not formed, and a space is formed between the thin film member and the elastic roller. When the elastic roller 13 rotates in the counterclockwise direction, the seamless thin film member 12 rotates following the rotation of the elastic roller 13 so that a portion having a space portion has an appropriate nip width and has an appropriate nip width.
Contact with weak contact pressure. As a result, a charging bias is evenly applied to the electrostatic latent image carrier, a stable and uniform charging potential is obtained, and the electrostatic latent image carrier is not damaged.

When a conventional rubber roller such as EPDM is directly used as a charging means, it is difficult to uniformly add a conductive material such as carbon powder to the rubber roller, and resistance unevenness occurs in the width direction of the charging roller. A large amount of charging current flows, and the amount of charge applied to the electrostatic latent image carrier becomes uneven, resulting in uneven density on the image. In addition, when the environment fluctuates, for example, at low temperature, low humidity, and high temperature and high humidity, the charging member fluctuates in resistance value, so that a shortage of charging current to the electrostatic latent image carrier and a variation in charging potential are observed. This problem can be improved by using a seamless thin film member having less resistance unevenness used in the embodiment. Here, in order for the elastic roller 13 and the seamless thin film member 12 to rotate without causing a slip, the kinetic friction coefficient between the elastic roller 13 and the seamless thin film member 12 is set to μ ₁ , and the kinetic friction coefficient between the seamless thin film member 12 and the support member 14 is set. when was the μ ₂ μ
And adjusting the surface roughness to be a _{1> μ 2.}

Elastic roller 13 and seamless thin film member 12
The elastic roller 13 made of a polyester fiber or the like having slidability shown in FIG.
And a rod-shaped member supporting both ends of the outside of the seamless thin film member 12, as shown in FIG. 3, an elastic roller 13, a rotatable urethane supporting both ends of the outside of the seamless member, and a foam such as an ethylene-propylene copolymer. As shown in FIG. 4, a roller-shaped member (support member 141) and a concentric semicircle member (support member) made of slidable polyester fiber or the like and weakly pressed from the outside of the seamless thin film member as shown in FIG. Member 142). These support members have the same length in the width direction as the charging member 1 and have a cleaning property. The support members form a space between the elastic roller and the seamless thin film member and carry a fog toner and an electrostatic latent image. In order to clean the seamless thin film member 12 contaminated with the shavings of the body 2, a decrease in the charging potential due to the contamination of the charging member due to the printing running, which could not be prevented by the cleaning bias when paper is not passed (between sheets). Can be avoided.

[0019]

As described above, the charging device of the present invention is provided with a seamless thin film member having a longer circumference than the elastic roller and forming a space at a portion facing the image carrier, thereby providing an image bearing device. When the nip width with the body is obtained, the surface of the electrostatic latent image carrier is not damaged because a weak pressing force is sufficient,
The torque of the device does not increase. Even if the nip between the charging member and the electrostatic latent image carrier during charging is non-uniform due to warpage, mounting error, twist, etc., the error is reduced by the space in the facing portion between the image carrier and the elastic roller. Since the light is absorbed by the bulging portion of the seamless thin film member including the portion, the charging bias can be applied uniformly, and the applied voltage is low and the ozone-less charging member can be supplied by a simple method.

Further, it is possible to prevent white spots and black stripes due to charging unevenness and discharge, which are disadvantages of a charging device using a brush or an elastic roller, and to prevent deterioration of charging characteristics due to abrasion of an electrostatic latent image carrier. A charging device capable of maintaining a high charging potential can be obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an image forming apparatus using a charging device according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of the charging member according to the embodiment of the present invention.

FIG. 3 is a sectional view of a charging member according to another embodiment of the present invention.

FIG. 4 is a sectional view of a charging member according to still another embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 1 charging member 2 electrostatic latent image carrier 3 toner hopper 4 toner 5 stirring member 6 toner supply member 7 toner carrier 8 thin layer forming member 9 transfer member 10 printing medium 11 cleaner unit 12 seamless thin film member 13 elastic roller 14 support member

Claims (1)

(57) [Claims] And a bias voltage contacting the electrostatic latent image carrier.
A charge is applied to the surface of the electrostatic latent image carrier by
In the charging device for charging, an elastic roller that is driven to rotate , and a peripheral length longer than a peripheral length of the elastic roller,
Tubular seamless thin film member provided outside the flexible roller
When the contact through the seamless thin film member to the elastic roller
The elastic roller and the electrostatic latent image carrier are opposed to each other.
Between the elastic roller and the seamless thin film member.
Forming a space portion, and forming the space portion
The outer surface of the seamless thin film member is in close contact with the electrostatic latent image carrier
And a support member for cleaning the surface of the seamless thin film member .
That the charging device.