JPH07113792B2 - Contact charging device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Object of the Invention [Field of Industrial Application] The present invention is a contact type in which a charging member to which a voltage is applied is brought into contact with the surface of the body to be charged (including static elimination). (Or a direct type) charging device.

[Conventional technology]

For convenience of description, the charging process of the photoconductor in the electrophotographic apparatus will be described as an example.

As is well known, the electrophotographic process includes the step of uniformly charging the surface of the photoconductor to a predetermined potential. For example, it is a uniform charging process for the surface of the photosensitive member prior to the formation of a latent image by exposure or the like. As the charging means, most of the electrophotographic apparatuses currently in practical use utilize a corona discharger having a wire electrode such as a gold-plated tungsten wire and a shield plate as main constituent members. That is, the corona generated by applying a high voltage to the wire electrode of the corona discharger is applied to the surface of the photoreceptor, which is the body to be charged, to charge the surface of the photoreceptor to a desired surface potential.

Although the charging treatment using a corona discharger has a good uniform charging property, it requires the application of a high voltage, it is inefficient in power consumption, and the wire and the inside of the discharger need to be cleaned quite frequently. There are many problems such as the occurrence of a considerably large amount of ozone and its by-products.

Therefore, recently, instead of using a corona discharger having many problems as described above, a contact (or direct) charging method, that is, a conductive member to which a voltage is applied is brought into contact with the surface of the body to be charged, is applied to the surface of the body to be charged. Various methods have been studied and proposed for directly injecting electric charges to perform charging treatment to a desired potential.

In the contact charging method, the voltage applied to the conductive member in order to obtain the desired charging potential on the surface of the body to be charged is the same as the charging potential using the corona discharger even in the case of the A-Si photoconductor with low charging ability. In order to obtain the voltage, a low potential, which is a fraction or less of the voltage that must be applied to the discharger, is sufficient, and power efficiency is good (for example, 800 to 2000 μA for charging by corona discharge).
/ DC6-8KV required 50-150μA / DC0.5-
1.5KV is sufficient), and the ozone generation is extremely small, so it is promising as a charging treatment method to replace the problematic corona discharge.

In particular, it is considered to be suitable as a charging treatment method for a material having high hardness (Vickers hardness of 1000 or more) and abrasion resistance such as an A-Si photoreceptor.

[Problems to be solved by the invention]

As a specific configuration mode of such a contact charging type device, there is a roller contact type. That is, the conductive member to be brought into contact with the surface of the body to be charged is a conductive elastic roller, the roller is rotatably supported and brought into pressure contact with the surface of the body to be charged by a pressing means, and a voltage is applied from a power source to the roller to be charged. The body surface is subjected to contact charging treatment.

The conductive elastic roller is required to elastically deform at the contact portion when brought into contact with the surface of the body to be charged with pressure in order to obtain good charging characteristics. In many cases, it is desired that such an elastic roller is easily elastically deformed and has a large contact portion area, and within that range, the contact pressure is almost uniform at any position. Further, the elastic roller may be rotating at a constant speed in some cases, and the contact portion will move at that time, but it is required that the contact pressure is always constant in terms of time.

Further, it is necessary to electrically have a predetermined electric resistance value.

As the elastic roller for the above-mentioned application, conventionally, a roller is used in which the elastic layer formed around the cored bar member serving as a shaft is made of, for example, a single material, and the material itself is made of low hardness rubber. Was there. However, in the case of the above-mentioned single solid low hardness rubber roller, it is known that strength and durability are deteriorated due to the weakness of the material itself when used for a long period of time, and there is a limit.

In addition, even if the hardness of the elastic material itself is low, in order to obtain a predetermined resistance value, carbon powder, carbon fiber,
When a conductive material such as metal powder or graphite is mixed, the hardness becomes high.
Therefore, a charging roller characterized by a two-layer structure of a low hardness base layer and a conductive surface layer as disclosed in Japanese Utility Model Publication No. 57-199349 has been proposed. However, such a two-layer roller has not been put into practical use because the manufacturing process becomes complicated and a problem is likely to occur in terms of adhesive strength between the base layer and the surface layer.

In view of the above, the present invention uses a conductive elastic roller having a predetermined resistance value, a single layer structure, low hardness, constant contact and excellent durability in the range of contact with the charged body, An object of the present invention is to provide an improved roller contact type practical contact charging device.

B. Configuration of the Invention [Means for Solving the Problems] The present invention is a conductive roller that contacts a charged body and charges the charged body, the conductive roller including an elastic layer and capable of applying a voltage. The contact charging device according to claim 1, wherein the elastic layer is provided with a through hole extending in the longitudinal direction of the conductive roller.

[Action]

Even if the elastic layer material itself has a hardness higher than the practical value by mixing a conductive substance into the elastic layer constituent material to obtain a predetermined resistance value, or the original hardness of the material is the practical value. Even if the hardness is higher than the above, the hardness of the conductive elastic roller itself can be lowered as desired by adopting the above-mentioned hole structure, and therefore the roller is pressed against the surface of the charged body with a stable pressing width. And a roller contact type improved practical contact charging device having good charging characteristics can be realized.

〔Example〕

FIG. 1 shows a very schematic structure of an example of a laser copying machine (LBP) equipped with a contact charging device according to the present invention.

Reference numeral 1 denotes a drum type photoconductor (eg, OPC photoconductor, A-Si photoconductor, etc.) which is rotationally driven in the direction of the arrow at a predetermined peripheral speed. In the course of its rotation, the photosensitive member is subjected to a uniform charging treatment of a positive or negative predetermined surface potential on its peripheral surface by a roller contact type charging device 2 which will be described later, and then an image exposure section 3 carries out a laser beam scanning exposure, not shown. Laser beam scanning image exposure L by means
By receiving the electrostatic latent image, electrostatic latent images corresponding to the exposure image pattern are sequentially formed. The latent image is toner-developed by the developing device 4, and the developed image is sequentially transferred to the surface of the transfer material P which is synchronously conveyed from the sheet feeding means (not shown) to the transfer charger 6 via the conveying portion 5. It The transfer material P that has received the image transfer is sequentially separated from the surface of the photosensitive member 1 by the separation charging device 7, is introduced into the image fixing means part (not shown) by the conveying part 8, and is printed out as an image formed product outside the apparatus. . The surface of the photoconductor after the image transfer is cleaned by the cleaning device 9, and then the pre-exposure device.
The entire surface is irradiated with light (charge-eliminating exposure, eraser) by 10, and then uniformly charged by the charging device 2 again to be repeatedly used for image formation.

The charging device 2 of this example is constructed as a unit that can be inserted into and removed from the copying machine. FIG. 2 is a perspective view showing a state in which the charging device unit is extracted and the roller side is faced up. Reference numeral 21 is a substrate, 22 and 22 are a pair of projecting pieces fixedly provided on the front and back ends of the back surface of the substrate, and 23 and 23 are shafts 23 on the respective projecting pieces.
A pair of levers that are freely rotatable around a ・ 23a, 24 ・ 24
Is a pressure spring that constantly urges the pair of levers to rotate clockwise about the shafts 23a and 23a, respectively.
A conductive elastic roller as a conductive member that rotatably supports a bearing between the arm portions on the side opposite to the side where the pressure springs are provided and is rotatably contacted with the surface of the photosensitive member 1 to directly charge the surface of the photosensitive member. is there. 26 is a grip for unit insertion / removal operation provided at the front end of the board 21, 27 is a power receiving connector provided at the rear end so as to project outward, 28 is a base fixed to the board 21, and a tip is provided. The portion is a power feeding brush whose elastic core is always in elastic contact with the shaft core 25a of the conductive roller 25, and the power feeding brush 28 and the power receiving connector 27 are electrically connected.

The charging device unit 2 has a substrate 21 between the guide rails 29, 29 (FIG. 1) on the copying machine main body side, with the conductive elastic roller 25 side facing downward and the power receiving connector 27 side first.
Engage both longitudinal edges of the conductive elastic roller 25 against the pressure springs 24, 24 so that the conductive elastic roller 25 does not come into sliding contact with the surface of the photosensitive member 1 and is received by a stopper (not shown). Push it into the machine until it is installed, and then attach it. Then, the conductive elastic roller 25 is brought into a free state. When the charging device unit 2 is mounted, the power receiving connector 27 is electrically connected to a power feeding connector (not shown) on the copying machine main body side, and the power feeding connector → power receiving connector 27 → power feeding brush 28 →
Conductive elastic roller 25
A predetermined voltage can be applied to. Roller 25
Is a conductive elastic layer that is an exterior by pressure springs 24
The outer surface of 25b is constantly kept in pressure contact with the surface of the photosensitive member with a predetermined pressure (for example, linear pressure of 0.01 to 0.2 kg / cm). The roller 25 rotates following the rotation of the photoconductor 1,
Even in the driven rotation process, the outer peripheral surface of the photoconductor 1 is constantly kept in pressure contact with a predetermined pressing force, and the power supply brush 28 is kept electrically connected to the shaft rod 25a.

FIG. 3 shows an enlarged cross-sectional view of the conductive elastic roller 25. The roller 25 includes a conductive shaft rod 25a as a core metal,
The conductive elastic layer 25b is integrally formed on the outer periphery of the conductive elastic layer 25b.

In the elastic layer 25b in this embodiment, a predetermined resistance value is obtained by mixing an electrically conductive material such as carbon powder, carbon fiber, graphite or metal powder into an elastic material such as silicone rubber or urethane rubber. In these elastic materials, the hardness of the material itself is generally increased by mixing the filler as described above, and the tendency is also observed in the material of the elastic layer 25b of the present embodiment. In the present invention, as described above, by providing the holes 25c in the elastic layer 25b, the increase in material hardness due to the above-mentioned conductivity can be reduced by the roller 25 itself.

The elastic layer 25b of the roller 25 of the present embodiment includes a cylindrical base layer portion 25d formed in contact with the shaft rod 25a, and a plurality of pillar walls 25e extending radially outward from the base layer portion 25d. , A cylindrical surface layer portion 25f connecting the pillar walls 25e. The pillar walls 25e are arranged at equal positions in the circumferential direction and extend substantially parallel to the shaft rod 25a in the axial direction. Thus, the pillar wall 25e, the outer surface of the base layer portion 25d, and the inner surface of the surface layer portion 25f form a plurality of holes 25c substantially parallel to the shaft rod 25a.

In this embodiment, the pillar wall 25e is a roller 25 as shown in FIG.
Is set asymmetrical with respect to the radius line a by having an inclination angle α with respect to the radius line a, and each hole 25c has an arbitrary radius line, for example, the radius line a _{1 in} FIG. It is formed so as to always penetrate the hole 25c. Above pillar wall 2
The inclination angle α of 5e and its thickness t are basically determined relatively so as to satisfy the above conditions, but in the actual design, including the above conditions, the thickness of the base layer portion 25d and the surface layer portion 25f and Together with this, the value is set so as to obtain a desired hardness of the elastic roller as a whole.

In this embodiment, the elastic roller 25 is the photosensitive member 1.
When it comes into contact with the pillar wall 25e, the pillar wall 25e is inclined, so that it is easily bent, and the roller as a whole is easily deformed. Moreover, the radius line a ₁ at an arbitrary angle is vacant so as to pass through any hole 25c. Since the holes are arranged, the deformation degree is almost the same at any position in the circumferential direction, and the surface layer part 25f with a constant thickness
Further uniformizes the degree of deformation in the circumferential direction. Moreover, even in such a state, the surface layer portion 25f secures a predetermined surface strength.

In this embodiment, the cross-sectional shape of each hole 25c is a deformed trapezoidal shape as shown in FIG. 3, but as another embodiment, the cross-sectional oblong shape as shown in FIG. Alternatively, a circular cross-sectional shape such as that shown in FIG. 5 may be used. Even in these cases, even if a conductive elastic material having a high material hardness is used as the material of the elastic layer 25b, a roller having a low hardness can be obtained. It is possible to obtain. Since the roller having the hole shape as shown in FIGS. 4 and 5 has a simple hole shape, it has an advantage that it is slightly easier to manufacture than the roller 25 having the hole shape as shown in FIG. . However, if the holes partially overlap the radial line as in the case of FIG. 4 or if there is no overlap area as in the case of FIG. 5, it is disadvantageous for lowering the hardness. Although the hardness is remarkably lowered as compared with the case where there is no hole, the lowering of the hardness is limited as compared with the case of FIG.

Specifically, a roller contact type charging device 2 as shown in FIG. 2 incorporating a conductive elastic roller 25 having the following cross-sectional shape as shown in FIG. 3 is reproduced as shown in FIG. The photoconductor 1 (OPC photoconductor with an outer diameter of φ60 mm) was mounted on the machine and charged.

Roller 25 specifications: Core 25a made of SUS with φ10 mm, conductive elastic layer 25b = outer diameter φ20 mm, resistivity 10 ^{5 to 8} Ωcm, material hardness 40
° (Asker C, 300g load), roller hardness 27 ° (same),
When the DC voltage of -700V was applied to the photosensitive member 1 at a total pressure of 2 kg in the dark and the peripheral speed was 66 mm / sec, the charging was successful. At this time, the pressing width N of the roller 25 to the photoconductor 1 was about 3 mm. After that, it was rotated at room temperature for 200 hours, but good charging was still possible and no change in the press contact width N was observed.

The contact charging by the roller has a feature that discharge is started in a continuous arbitrary gap due to a difference in curvature between the photoconductor 1 and the roller 25, and the discharge is stably maintained in a constant gap region by an applied voltage. In the case of the brush method, the point contact is aggregated, whereas in the roller method, the elastic roller is pressed into contact with the photosensitive member and the positioning of the gap etc. for stable surface contact is stable, and the end discharge does not depend on the durability. improves.

By using the elastic roller, the followability with respect to the photoconductor is improved, and the gap due to the difference in curvature is stabilized.

Silicone rubber or urethane rubber can be used as the material of the elastic layer 25b of the roller 25, but it is preferable to select urethane rubber rather than silicone rubber from the viewpoint of preventing uneven charging due to oil oozing out and abrasion resistance. . By using urethane rubber, it becomes easy to make the conductive roller 25 have a relative speed difference with the photoconductor 1, and it is possible to reduce charging unevenness due to rotation rattling of the roller 25, or to adhere to the photoconductor surface by rubbing. It produces the effect of scraping off traces of corona products.

It was found that by raising the resistance value to 10 ⁵ to 10 ⁶ Ω, high-quality images can be obtained without preventing dielectric breakdown and without uneven charging. Especially in the case of A-Si photosensitive member, a protective resistance effect of rush current to the abnormal growth portion peculiar to A-Si photosensitive member called spherical protrusion is created, and the resistance is not too high and uneven supply voltage does not occur, Compared to other photoconductors, A-Si has a current that nearly doubles even with the same roller contact charging
The photoconductor makes it a very suitable contact charging roller.

In the case of charging with a roller, a standard dark area potential of 400 V, for example, is obtained on the surface of the photoconductor, but an applied voltage of about 1/10 that in the case of using a corona discharger is sufficient. In the case of the roller charging device 2, the current amount is actually suppressed to about 1/5 that in the case of the corona discharger, and as a result, the amount of ozone generated is about 40 ppm in the case of the corona discharger. In case of roller charging, it decreased to about 3ppm.

The voltage applied to the roller 25 may be only DC (direct current), but better results can be obtained with a DC + AC voltage in which an AC (alternating current) component is superimposed on a DC component.

DC component 500-1000V and AC component 800-1800Hz, 800-1800V _PP
By applying the DC + AC superimposed voltage of, good images without uneven charging were obtained.

Particularly V _PP is effective, it is possible to cover the dirt conductive roller 25 when more than 1400 V _PP, almost eliminating the accompanying charging unevenness roller rotation.

C. Effect of the Invention As described above, in the roller contact type charging device, by providing holes in the elastic layer of the roller, a conductive substance is mixed into the elastic layer constituent material in order to obtain a predetermined resistance value. Even if the hardness of the elastic layer material itself is higher than the practical value, or even if the hardness of the original material is originally higher than the practical value, the hardness of the roller itself can be lowered to a desired value. Therefore, the roller can be brought into a pressure contact state with a stable pressure contact width with respect to the surface of the body to be charged, and a roller contact type improved practical contact charging device having good charging characteristics can be realized. The intended purpose is often achieved.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an example of a laser copying machine equipped with a roller contact type charging device according to the present invention, FIG. 2 is a perspective view of the charging device with the roller side facing upward, and FIG. An enlarged transverse sectional view and FIGS. 4 and 5 are enlarged transverse sectional views of other roller examples, respectively. 1 is a rotating drum type photoconductor, 2 is a roller contact type charging device,
Reference numeral 25 is a conductive elastic roller, 25a is a shaft rod as a metal core of the conductive elastic roller, 25b is an elastic layer externally mounted on the shaft rod, and 25c is a hole provided in the elastic layer.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Junji Araya 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (56) Reference JP-A-62-244860 (JP, A) 57-199349 (JP, U)

Claims (1)

[Claims] 1. A contact charging device, comprising a conductive roller that contacts a charged body and charges the charged body, the conductive roller having an elastic layer and capable of applying a voltage, wherein the elastic layer is the conductive layer. A contact charging device comprising a through hole extending in the longitudinal direction of the roller.