JPS63208879A - contact charging device - Google Patents

Abstract

PURPOSE:To obtain a conductive elastic roller which has low hardness, assures constant contact and has excellent durability by forming plural holes approximately at equal intervals to the inside of the elastic layer of said roller in the circumferential direction of the roller so as to extend in the longitudinal direction thereof. CONSTITUTION:The holes 25c are provided to the elastic layer 25b of the conductive elastic roller 25 as a conductive member which contacts the surface of a photosensitive body 1 to directly and electrically charge said surface. Then, the hardness of the roller 25 itself can be lowered to a desired level by adopting the hole structure to said roller even if a conductive material is incorporated into the elastic layer 25b in order to obtain a prescribed resistance value and the hardness of the elastic layer material itself is eventually increased to a practicable use value or above. The roller 25 is, therefore, brought into a pressurized contact state with the surface of the object 1 to be charged with a stable pressurized contact width.

Description

Detailed Description of the Invention A. Purpose of the Invention [Industrial Field of Application] The present invention relates to a contact method for charging (including removing static electricity) the surface of a charged object by bringing a conductive member to which a voltage is applied to the surface of the charged object into contact with the surface of the charged object. formula(
or direct type) charging device.

(Prior Art) For convenience of explanation, charging processing of a photoreceptor in an electrophotographic apparatus will be described as an example.

As is well known, the electrophotographic process includes a step of uniformly charging the surface of a photoreceptor to a predetermined potential.

For example, this may include uniform charging treatment of the photoreceptor surface prior to forming a latent image by exposure or the like. As the charging means, most electrophotographic apparatuses currently in practical use use a corona discharger whose main components are a wire electrode such as a gold-plated tungsten wire and a shield plate. That is, by applying a high voltage to the wire electrode of the corona discharger, corona generated is applied to the surface of the photoreceptor, which is the object to be charged, so that the surface of the photoreceptor is charged to a desired surface potential.

Charging treatment using a corona discharger has good uniform charging properties, but it requires the application of high voltage, has poor power efficiency, requires cleaning the wire and the inside of the discharger quite frequently, and has problems associated with corona discharge. However, there are many problems such as the generation of quite large amounts of ozone and its by-products.

Therefore, recently, instead of using a corona discharger which has many problems as mentioned above, a contact (or direct) charging method has been introduced, in other words, a method of charging the surface of the charged object by bringing a conductive member to which a voltage is applied into contact with the surface of the charged object. Various methods have been researched and proposed for charging the device to a desired potential by directly injecting charge.

In the contact charging method, the voltage applied to the conductive member in order to obtain a desired charging potential on the surface of the charged object is A-9i, which has a low charging ability.
In the case of a photoreceptor, a low potential of a fraction or less of the voltage that must be applied to a corona discharger to obtain a similar charging potential is sufficient, resulting in good power efficiency ( For example, when charged by corona discharge, 800~
2000 L A/DC■What used to require 6-8 KV is now 50-150 L A/ace O, 5-1.5 KV
This method has advantages such as generating only a small amount of ozone, and is an effective charging treatment method in place of corona discharge, which has many problems.

Especially high hardness (Vickers hardness!) like A-5i photoconductor.
000 or more) φ This is considered to be an appropriate charging treatment method for materials with excellent wear resistance.

[Problem that the invention seeks to solve]

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

In order to obtain good charging characteristics, the conductive elastic roller described above is required to be elastically deformed at the contact portion when it is brought into contact with the surface of a charged object under pressure. In most cases, such elastic rollers are desired to be easily elastically deformed, have a large contact area, and have nearly uniform contact pressure at any position within that range. Further, such an elastic roller may be rotating at a constant speed, and in this case, the contact portion moves, but it is required that the contact pressure is always constant over time.

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

Conventional elastic rollers for the above applications.

Rollers have been used in which the elastic layer formed around the core metal member serving as the shaft is made of, for example, a solid solid material, and the material itself is low hardness rubber. However, in the case of the above-mentioned single solid low hardness rubber roller, it is known that the strength and durability deteriorate due to the weakness of the material itself when used for a long period of time, and there is a limit thereto.

In addition, even if the hardness of the elastic material itself is low, carbon powder, carbon fiber, or
When a conductive material such as metal powder or graphite is mixed, the hardness increases, which is a disadvantage.

Therefore, a charging roller characterized by a two-layer structure consisting of a low hardness base layer and a conductive surface layer has been proposed as disclosed in Japanese Utility Model Application Publication No. 57-199349. However, the manufacturing process for such a two-layer roller becomes complicated, and
Problems also tend to occur in terms of adhesive strength between the base layer and the surface layer, so it has not been put into practical use.

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

1. Configuration of the Invention [Means for Solving Problems] In the present invention, a conductive elastic roller is rotatably supported, and the roller is pressed against the surface of the charged object by a pressure means.

In a contact charging device that charges the surface of a charged body by applying a voltage to the roller, a plurality of electrification devices are provided in the elastic layer of the conductive elastic roller, extending in the longitudinal direction of the roller and existing at approximately equal intervals in the circumferential direction of the roller. The object of the present invention is to provide a contact charging device characterized by having voids formed therein.

[For production]

Even if a conductive substance is mixed into the material constituting the elastic layer in order to obtain a predetermined resistance value, and as a result, the hardness of the clavicular layer material itself becomes higher than the practical value, or the original hardness of the material exceeds the practical value. Even if the hardness of the conductive elastic roller itself is higher than the above, the hardness of the conductive elastic roller itself can be lowered as desired by using the upper chamber hole structure. It is possible to realize an improved and practical roller contact type contact charging device that can be brought into pressure contact state and has good charging characteristics.

〔Example〕

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

l is a drum-type photoreceptor (e.g., OPC photoreceptor, A-9i photoreceptor, etc.) that is rotated at a predetermined circumferential speed in the direction of the arrow. During the rotation process, the photoreceptor is charged by a roller contact type described later. ? At t12, the peripheral surface is uniformly charged to a predetermined positive or negative surface potential, and then subjected to laser beam scanning image exposure by a laser beam scanning exposure means (not shown) in the image exposure section 3, thereby forming an exposed image pattern. Electrostatic latent images corresponding to the images are sequentially formed. The latent image is developed with toner in a developing device 4, and the developed image is sequentially transferred onto the surface of a transfer material P that is synchronously conveyed from a paper feeding means section (not shown) to a transfer charger section 6 via a conveying section 5. Ru. The transfer material P that has undergone the image transfer is sequentially separated from one surface of the photoreceptor by the separation charger 7, is introduced into an image fixing means (not shown) in the conveying section 8, and is printed out outside the machine as an image formed product. . After the image transfer, the photoreceptor surface is cleaned by a cleaning device 9, and then the entire surface is irradiated with light (static charge removal exposure, eraser) by a pre-exposure device IO.
The photosensitive material is then uniformly charged again by the charging device 2 and is repeatedly used for image formation.

The charger M2 in this example is configured as a unit that can be inserted into and removed from the copying machine. FIG. 2 is a perspective view of the charging device unit taken out and with the roller side facing up. Reference numeral 21 denotes a board; 22 and 22 are a pair of protrusions fixed to the front end and the rear end of the back surface of the board; and 23 and 23 are provided to each of the protrusions so as to be freely rotatable about shafts 23a and 23a. The pair of levers 24 and 24 are respectively connected to the shaft 23.
A pressure spring 25 is rotatably supported by a bearing between the side of each lever 23-23 on which the pressure spring is provided and the chest on the opposite side.
This is a conductive elastic roller serving as a conductive member that comes into contact with one surface of the photoreceptor and directly charges the surface of the photoreceptor. 26 is the substrate 21
A grip handle for inserting and removing the unit is provided on the front end of the
Reference numeral 27 denotes a power receiving connector provided at the rear end so as to protrude outward; and 28, the base is fixed to the substrate 21, and the tip is always elastically in contact with the shaft rod 25a, which is the conductive core of the conductive roller 25. The power feeding brush 28 and the power receiving connector 27 are electrically connected to each other.

The charging device unit 2 is placed between the guide rails 29 and 29 (FIG. 1) on the side of the copying machine with the conductive elastic roller 25 side facing downward and the power receiving connector 27 side first. Both longitudinal edges are engaged, and the conductive elastic roller 25 is released upward against the pressure springs 24-24 so as not to come into sliding contact with the surface of the photoreceptor 1, and is received by a stopper (not shown). Then, the conductive elastic roller 25 is set in a free state. In this installed state of the charging device unit 2, the power receiving connector 27 is electrically connected to a power feeding connector (not shown) on the side of the copying machine, and the path of the power feeding connector → power receiving connector 27 → power feeding brush 28 → shaft rod 25a Then, a predetermined voltage can be applied to the conductive elastic roller 25 from the power supply on the machine side. Also, the roller 25 is connected to the pressure spring 24.
24, the outer surface of the conductive elastic layer 25b, which is the exterior, is applied with a predetermined pressing force (for example, a linear pressure of 0°01 to 0°) against the surface of the photoreceptor.
．． 2kg/c■) and is maintained in a state of pressure contact at all times. The roller 25 rotates in accordance with the rotation of the photoreceptor 1, and even during the rotation process, the roller 25 is always kept in pressure contact with the outer peripheral surface of the photoreceptor 1 with a predetermined pressure, and the power supply brush 28 is connected to the shaft rod 25a. remains electrically conductive to the

FIG. 3 shows an enlarged cross-sectional view of the conductive elastic roller 25, which has a conductive shaft rod 25 as a core metal.
a, and a conductive elastic layer 25b integrally formed on its outer periphery.
It consists of

The elastic layer 25b in this embodiment obtains a predetermined resistance value by mixing an elastic material such as silicone rubber or urethane rubber with a conductive material such as carbon powder, carbon fiber, graphite, or metal powder. As mentioned above, in these elastic materials, the hardness of the material itself is generally increased by mixing a filler.
This tendency was also seen in the material b. 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 electrical conductivity is suppressed.
It became possible to make it smaller.

The elastic layer 25b of the roller 25 of this embodiment includes a cylindrical base layer portion 25d formed in contact with the shaft rod 25a, and a plurality of support walls 25e extending radially outward from the base layer portion 25d.
and a cylindrical surface layer portion 25f that connects each support wall 25e. The support walls 25e are arranged at equal positions in the circumferential direction and extend in the axial direction substantially parallel to the shaft rod 25a.

Thus, a plurality of holes 25c substantially parallel to the shaft rod 25a are formed by the support wall 25e, the outer surface of the base layer portion 25d, and the inner surface of the surface layer portion 25f.

In this embodiment, the support wall 25e is set asymmetrically with respect to the radius line a by having an inclination angle α with respect to the radius 1aa of the roller 25, as shown in FIG.
c is formed so as to always pass through the hole 25c at any corner of an arbitrary radius line, such as radius line a in the figure. The inclination angle α and the thickness t of the support wall 25e are basically determined relative to each other so as to satisfy the above conditions, but in actual design, the above conditions must be included in the base layer portion 25d and the surface layer portion 25f. Together with the thickness of the elastic roller, it is determined to a value that provides the desired hardness of the elastic roller as a whole.

In this embodiment, when the elastic roller 25 comes into contact with the photoreceptor l, since the supporting wall 25e is inclined, it is easy to pile up, and the roller as a whole is easy to deform, and moreover, it can be moved at any angle. The radius line al is always one of the holes 25
Since the holes are arranged so as to penetrate through c, the degree of deformation is approximately the same at any position in the circumferential direction, and the surface layer portion 25f having a constant thickness further equalizes the degree of deformation in the circumferential direction. Moreover, even in such a state, the surface layer portion 25f maintains 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 shape may be an oval shape as shown in FIG. Alternatively, the cross section may have a circular shape as shown in FIG. It is possible to obtain. A roller having a hole shape as shown in FIGS. 4 and 5 has a simple hole shape, so it has the advantage of being slightly easier to manufacture than the roller 25 having a hole shape as shown in FIG. 3. . However, if the pores partially overlap with the radius line as in the example in Figure 4, or if there is no overlapping area at all as in the example in Figure 5, it is disadvantageous to lower the hardness, and the pores Although the hardness is much lower than that without it, there is a limit to how hard it can be lowered than the example shown in FIG.

Specifically, the roller contact type charging device 2 as shown in FIG. 2, which incorporates a conductive elastic roller 25 having the cross-sectional shape as shown in FIG. The photoreceptor 1 (OPC photoreceptor with an outer diameter of 60 mm) was charged with the photoreceptor 1 attached to the machine.

Specifications of the roller 25: Core metal 25a = made of SUS with φ1oss, conductive elastic layer 25b = outer diameter φ20 l, resistivity 105
~8Ωawe Material hardness 40° (Asker 〇, 300g load Ir!-) - Roller hardness 27° (same), total pressure in contact with photoreceptor 1 = 2kg DC voltage -700V was applied in a dark area, peripheral speed 8B + sm /
When rotated with see, good charging was achieved. At this time, the pressing width N of the roller 25 against the photoreceptor 1 was approximately 3 cm. After that, it was rotated for 200 hours at room temperature.
Good charging was still possible, and no change in the pressure contact width N was observed.

Contact charging by the roller starts discharging at any continuous gap due to the curvature difference between the photoreceptor 1 and the roller 25,
It has the characteristic that a certain gap region maintains stable discharge depending on the applied voltage. In the case of the brush method, it is a collection of point contacts, whereas in the roller method, the elastic roller is pressed against the photoreceptor to achieve surface contact, which stabilizes the positioning of gaps, etc., and also increases durability because it does not depend on tip discharge. Go towards F.

By using an elastic roller, the ability to follow the photoreceptor is improved, and the gap caused by the difference in curvature is also stabilized.

The material of the elastic layer 25b of the roller 25 can be silicone rubber or urethane rubber, but urethane rubber is preferred over silicone rubber in order to prevent uneven charging due to oil seepage and from the viewpoint of wear resistance. By using urethane rubber, which is preferable, it is easy to make the conductive roller 25 have a relative speed difference with the photoreceptor 1, and uneven charging due to rotational play of the roller 25 can be reduced.
The rubbing effect produces the effect of scraping off minute corona products adhering to the surface of the photoreceptor.

It has been found that by increasing the resistance value to 10 5 to 10 6 Ω, dielectric breakdown can be prevented, and high quality images can be obtained without uneven charging. In particular, in the case of A-Si photoreceptors, a protective resistance effect of rush current is created to the abnormal growth part unique to A-Si photoreceptors called 1 spherical protrusion, and there is no possibility that the resistance is too high and causes uneven supply voltage. The A-5i photoreceptor, in which nearly twice as much current flows even with the same roller contact charging than a low-temperature photoreceptor, makes it an extremely suitable contact charging roller.

In the case of charging with a roller, in order to obtain a standard dark potential of 400 V on the surface of the photoreceptor, the applied voltage is actually about 1/10 of that of a corona discharger, and the amount of current is limited by the roller charging device. In the case of 2, the amount of current is actually limited to about 20% compared to the case of a corona discharger, and as a result, the ozone bag generated was 40pp in the case of the corona discharger, whereas in the case of roller charging it was about 3pp. ppm.

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

DC component 500~1000V and AC component 800~1
800Hz, 800~teoov pp DC+AC
By applying a superimposed voltage, a good image without uneven charging was obtained.

In particular, v pp is very effective, and when it is 1400 V pp or more, it can cover dirt on the conductive roller 25 and almost eliminate charging unevenness caused by rotation of the roller.

C. Effects of the Invention As described above, by providing holes in the elastic layer of the roller in a roller contact type charging device, a conductive substance is mixed into the material constituting the elastic layer in order to obtain a predetermined resistance value. Even if the hardness of the clavicular 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 as desired. Therefore, it is possible to bring the roller into pressure contact with the surface of the object to be charged with stable pressure contact radius, and it is possible to realize an improved and practical roller contact type contact charging device having good charging characteristics. The intended purpose is well achieved.

[Brief explanation of the drawing]

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. 4 and 5 are enlarged cross-sectional views of other roller examples, respectively. 1 is a rotating drum type photoreceptor, 2 is a roller contact type charging device,
25 is a conductive elastic roller; 25a is a shaft serving as a metal core thereof; 25b is an elastic layer sheathed thereon; and 25c is a hole provided in the elastic layer. Figure 4 Figure 5 Figure 1

Claims (1)

[Claims] (1) A contact charging device that rotatably supports a conductive elastic roller, presses the roller against the surface of the object to be charged by a pressure means, and charges the surface of the object to be charged by applying a voltage to the roller, the conductive A contact charging device characterized in that a plurality of holes are formed in the elastic layer of the elastic roller, extending in the longitudinal direction of the roller and being present at approximately equal intervals in the circumferential direction of the roller.