JPS63208878A - Electric charger - Google Patents

Abstract

PURPOSE:To permit a stable and uniform electric charge treatment by using a specific conductive rubber material to form a surface material of a conductive member, which material contacts a surface of an object to be electrically charged. CONSTITUTION:A conductive roller 25 consists of a shaft bar 25a as a metallic arbor and a conductive rubber material layer 25b which is integrally mounted thereon and has 15-80 deg. rubber hardness and 10<5>-10<6>OMEGA electric resistance value. The always stable and uniform electric charge treatment of the surface of the photosensitive body 1 which is the object to be charged is permitted if the surface of said object to be charged is subjected to the contact charge treatment by bringing the above-mentioned conductive rubber material 25b into contact with the surface of the object to be charged. Stable outputting of the image having good quality is possible with a device for forming the image by subjecting the photosensitive body 1 to the charge treatment.

Description

[Detailed description of the invention] B. Purpose of the invention [Industrial application field] The present invention relates to a charging device.

More specifically, the present invention relates to a contact-type (or direct-type) charging device that charges (including neutralizes) the surface of a charged object by bringing a conductive member applied with a voltage into contact with the surface of the charged object.

[Conventional technology]

For convenience of explanation, the charging process 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, W! due to exposure etc. This includes uniform charging treatment of the photoreceptor surface, etc., performed prior to image formation. 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.

Although charging treatment using a corona discharger has good uniform charging properties, it has the following problems.

1) Application of high voltage In order to obtain a surface potential of, for example, 500 to 700 V to the photoreceptor, it is necessary to apply a high voltage of 0.04 to 8 KV to the wire electrode. Maintain a large distance between the wire electrode and the shield plate to prevent leakage to the shield plate and main body (
5 to 8 mm or more), the discharger itself becomes larger and the use of highly insulated cables becomes essential.

2) Most of the discharge current from the wire electrode with poor power efficiency flows to the shield plate,
The corona current flowing toward the photoreceptor, which is the charged object, is only about 5 to 30% of the total discharge current, and the power efficiency is poor.

3) Wire dirt Wire electrode with large curvature to increase discharge efficiency (generally, wire electrodes with a diameter of 60 to 100 #Lm are used)
However, the high electric field formed on the wire surface collects fine dust such as toner particles φ paper fiber pieces and corona discharge products inside the device, and the wire surface becomes dirty. Wire contamination tends to cause uneven discharge, which causes image unevenness, white spots, black lines, etc. Therefore, it is necessary to clean the wires and the inside of the discharger quite frequently.

4) Generation of corona discharge products A considerable amount of ozone is generated due to corona discharge.

Ozone oxidizes nitrogen in the air to produce nitrogen oxides (NOx)
etc. Furthermore, the produced nitrogen oxides react with moisture in the air to produce nitric acid and the like. Corona discharge products such as ozone and its by-products such as nitrogen oxides and nitric acid adhere to or act on the photoreceptor surface and surrounding equipment surfaces, causing alteration and deterioration of the photoreceptor surface and oxidation of the equipment. cause Adhesion of corona discharge products to the photoreceptor surface lowers the resistance of the photoreceptor surface, lowering the charge retention ability and causing image blurring. In addition, the corona discharge products adhering to the inner surface of the shield plate of the corona discharger volatilize and liberate not only when the electrophotographic device is in operation but also during rest periods such as at night, and this corresponds to the discharge opening of the discharger. It adheres to the surface of the photoreceptor and lowers the resistance of that portion of the photoreceptor. For this reason, it is well known that in the first copy that is first output when the device is restarted, image blurring occurs in the portion corresponding to the opening of the discharger while the device is inactive.

The photoreceptor used is an amorphous silicon photoreceptor (hereinafter referred to as A-S).
(abbreviated as i photoreceptor), the above-mentioned problems caused by corona discharge products become especially serious. That is, the A-5i photoreceptor has a lower charging ability than other CdJ-resin dispersion system, ZnO-resin dispersion system, Se-vapor deposition system, 5e-Te deposition system, OPC system, etc. Charging treatment using corona discharge for the -5i photoreceptor is configured to significantly increase the amount of discharge (charging) current than in the case of other photoreceptors as described above.

A-Si photoreceptors are often used especially in high-speed electrophotographic equipment, and the amount of discharge current in such cases is 2000 IL.
Some even reach A. Since there is a proportional relationship between the amount of discharge current and the amount of ozone generated, the amount of ozone generated is particularly large in a system where the photoreceptor is an A-9i photoreceptor and is charged by corona discharge, and therefore the amount of ozone generated is large. The problem caused by the generation of discharge products becomes particularly large.

In order to prevent or reduce the harmful effects caused by corona discharge products as described above, fan means for actively eliminating generated ozone,
IJm of absorption/decomposition filter means, drum heater means, etc.
It is necessary to equip the equipment with the following.

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 in which charging is performed to a desired potential by directly injecting charges.

For example, a method of charging a photoconductor by bringing a voltage-applied brush into contact with it (JP-A-513-104348, No. 57
-87951), a charging method in which multiple voltage application contacts are brought into contact (JP-A-58-139156), while simultaneously reducing the amount of ozone and polishing the photoreceptor surface to actively eliminate image blur. Charging method (JP-A-58-15097
No. 5), and other Japanese Patent Application Laid-open Nos. 178287-1987 and 56-
104351, No. 58-405H, etc.

In the contact charging method, in order to obtain a desired charging potential on the surface of the charged object, the voltage applied to the conductive member is set at a low A-5i of the charging part.
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 ILA 10n 6 to 8 KV is required, but 50 to 150 uLA/DCe O, 5 to 1.5 V is sufficient), it has the advantage of generating very little ozone, and it solves the problem. This is a promising charging treatment method to replace the commonly used corona discharge.

It is considered to be particularly suitable as a charging treatment method for materials such as A-Si photoreceptors which have high hardness (Vickers hardness of 1000 or more) and excellent wear resistance.

[Problem that the invention seeks to solve]

However, despite the various advantages of the contact charging method as described above, a practical device such as an electrophotographic device incorporating a charging device utilizing the contact charging method has not yet appeared.

A major reason for this is the lack of stability in uniform charging treatment. In other words, uneven contact of contacts such as brushes,
In practice, it is easy to see so-called uneven charging due to resistance mismatching with the photoreceptor.

In the case of an A-S i photoreceptor, uneven charging and dielectric breakdown problems are more likely to occur due to the presence of defective portions of the photoreceptor called spherical protrusions.

In the case of the A-9i photoreceptor, there are a blocking type and a single layer high resistance type. The blocking type has a charge injection blocking layer, a photosensitive layer, and a surface protective layer laminated in this order on a substrate such as Al. The charge injection blocking layer blocks the injection of electrons, and the surface protective layer blocks the injection of holes. plays a role. Since this blocking type allows the photosensitive layer to be made pure, it is possible to take effective measures against optical memory and photodeterioration. The high-resistance type is one in which the A-Si layer is doped with oxygen or the like to make the resistance high and has charge retention properties.

The A-9i photoreceptor, both blocking type and high resistance type, is extremely superior in deterioration resistance, abrasion resistance, hardness, scratch resistance, impact resistance, etc., compared to other photoreceptors. Therefore, even if the A-Si photoreceptor is pressed against a conductive member for charging, its characteristics deteriorate due to crystallization of the photosensitive layer.

There are no problems such as indentations, scratches, abrasion, or adhesion, staining, or deterioration due to chemical reactions with the surface material of the conductive member, and there are no problems such as mechanical contact and release of the conductive member against the photoreceptor. It is also resistant to impact effects.

However, in the case of the A-Si photoconductor, when the surface is actually charged by contact, the spherical protrusions that tend to cause uneven charging due to the presence of so-called minute spherical protrusions that are formed to some extent on the A-9i photoconductor during manufacturing. Withstand voltage (DC) of 500~
Since the dielectric breakdown is about too much, it is easy to see dielectric breakdown at the spherical protrusion portion, and when dielectric breakdown occurs, the entire charge in the axial direction of one breakdown point flows to that breakdown point and is no longer charged. There is a problem with this.

The A-Si layer is generally formed by decomposing and depositing silane gas using various CVD methods using light, heat, RF, or the like as an energy source. Currently, from the viewpoint of characteristics and cost, A-
9i photoreceptors have been manufactured. At this time, if there is dust or uneven parts on the substrate-E, the A-9t film that is deposited on the substrate will grow abnormally partially using those parts as nuclei, causing defective parts of the photoreceptor called spherical protrusions. do. At present, it is practically unavoidable that some occurrence of such spherical protrusions occurs.

The present invention has been researched and developed in view of the above problems, and is capable of stably and uniformly charging the surface of a charged body using a contact charging method. The object of the present invention is to realize a practical device that is equipped with a contact charging device that has various advantages as described above in place of an electric appliance.

1. Structure of the Invention [Means for Solving Problems] The present invention is a contact charging device that charges 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. The material of the surface material of the conductive member that comes into contact with at least the surface of the charged object has a rubber hardness of 15 to 80 degrees (JIS Hs
), the charging device is characterized by being made of a conductive rubber material having an electrical resistance value of 105 to 106 Ω.

[For production]

That is, the material of the surface material of the conductive member that comes into contact with at least the surface of the charged object has a rubber hardness of 15 to 80 degrees and an electrical resistance value of 10.
If a conductive rubber material with a resistance of 5 to 106 Ω is used and contact charging is performed by bringing it into contact with the surface of the object to be charged, the surface of the object to be charged can always be stably and uniformly charged, as shown in the examples below, and the photoreceptor can be charged. The present invention was completed based on the discovery that images of good quality can be stably output in an image forming apparatus.

〔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 photoreceptor that is rotated at a predetermined circumferential speed in the direction of the arrow, and in the case of one example, it is an A-9i photoreceptor. During the rotation process, the photoreceptor is uniformly charged to a predetermined positive or negative surface potential on its circumferential surface by a roller-type contact charging device N2, which will be described later.Then, the image exposure unit 3 scans the photoreceptor with a laser beam (not shown). By receiving laser beam scanning image exposure by the exposure means, electrostatic latent images corresponding to the exposed image pattern are sequentially formed. The latent image is developed with toner in a developing device 4, and the developed image is transferred from a paper feeding section (not shown) to a conveying section 5.
The images are sequentially transferred onto the surface of the transfer material P, which is synchronously conveyed to the transfer charger section 6 via the transfer charger section 6. 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 conveyance section 8, and is printed out outside the machine as a single image formation. . After the image has been transferred, the surface of the photoreceptor is cleaned by a cleaning device 9, then subjected to full-surface light irradiation (discharge exposure, eraser) by a pre-exposure device 10, uniformly charged again by a charging device 2, and repeatedly used for image formation. Ru.

The charging device 2 in this example is of a roller type and is configured as a unit that can be inserted and removed from the copying machine (hereinafter referred to as the roller charging device). Fig. 2 shows the roller charging device unit taken out. FIG. 3 is a perspective view 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. A pair of levers 24 and 24 each have a shaft 2.
Pressure springs 3a and 23a are always rotated in a clockwise direction, and 25 is a photosensitive sensor rotatably supported by a bearing between the arms of each lever 23 and 23 on the side opposite to the pressure springs. The conductive roller 25 of this example, which is a roller (hereinafter referred to as a conductive roller) as a conductive member that directly charges the surface of the photoreceptor by contacting the surface of the photoreceptor, has a shaft rod 25 as a metal core.
a, and an electrically conductive rubber material layer 25b having a rubber hardness of 15 to 80 degrees and an electrical resistance value of 105 to 106 Ω, which is integrally packaged therewith. Reference numeral 26 indicates a grip handle for inserting and removing the unit, which is provided at the front end of the board 21, 27 is a power receiving connector, which is provided at the back end and projects outward, and 28, the base is fixed to the board 21, and the tip This is a power supply brush whose part is always elastically in contact with the shaft 25a of the conductive roller 25, and this power supply brush 2
8 and the power receiving connector 27 are electrically connected.

The roller 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 roller 25 side facing downward and the power receiving connector 27 side first. Both edges are engaged, and the conductive roller 25 is released upward against the pressure spring 241124 so as not to come into sliding contact with the surface of the photoreceptor 1, until it is received by a stopper (not shown). Then, the conductive roller 25 is set in a free state. When the roller charging device unit 2 is installed, the power receiving connector 27 is electrically connected to the power feeding connector (not shown) on the side of the copying machine, and the power feeding connector → the power receiving connector 27
A predetermined voltage can be applied to the conductive roller 25 from the power source of the machine through the path of → power supply brush 28 → shaft rod 25a.

Further, the conductive roller 25 is pressed by a pressure spring 24-24 so that the outer surface of the conductive rubber material layer 25b, which is the exterior, is applied to the surface of the photoreceptor 1 with a predetermined pressure (for example, a linear pressure of 0.01 to 0.2 kg/
cm) and are kept in constant pressure contact. The conductive roller 25 in the last example rotates in accordance with the rotation of the photoreceptor 1, and even during the rotation process, it 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 maintained in electrical continuity with the shaft rod 25a.

Contact charging by the roller starts discharging at any continuous gap due to the difference in curvature 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, a rigid roller is brought into pressure contact with the photoconductor, and the positioning of gaps, etc. for surface contact is stable, and there is no tip discharge. Durability is also improved.

a. Charging Capacity As shown in Figure 1, an existing laser copying machine uses a rotating drum-type A-9i photoconductor as a photoconductor, and the surface of the photoconductor is uniformly primary charged with a corona discharger (Canon Co., Ltd.). MP
9030.30 cp layer, process speed 180mm
/5ec), charging by a corona discharger, and charging by removing the corona discharger and attaching a roller charging device 2 which is a contact charging device as shown in Figures 1 and 2 above. We investigated the difference in ability between

The results are shown in the graph in Figure 3. The horizontal axis is the roller charging device N.
The voltage applied to the shaft rod 25a of the conductive roller 25 of No. 2 or the voltage applied to the corona charging wire of the corona discharger, and the vertical axis is the surface potential of the photoreceptor l at the developing position. A is the case of charging by the roller charging device 2, and B is the case of charging by the corona discharger. Standard dark potential on photoreceptor surface
It can be seen that in order to obtain a potential of 400 V, when using the roller charging device 12, the applied voltage is about 1/10 of that when using the corona discharger.

b. Amount of current - amount of ossine generated, or the relationship between the current value from the power supply (horizontal axis) and the photoreceptor surface potential (vertical axis) in both cases of charging by the roller charging device 2 and charging by the corona discharger. Examined. A is the case of charging by the roller charging device 2, and B is the case of charging by the corona discharger. It can be seen that the amount of current when a potential of 400 V, which is a standard dark potential, is obtained on the surface of the photoreceptor is suppressed to about the same amount of current when using the roller charging device 2 as when using the corona discharger. As a result, while the amount of ozone generated was 40 ppm in the case of the corona discharger, it was reduced to about 3 ppm in the case of the roller charging device 2.

C. Roller material: Roller charging device! ! Regarding 2, the exterior 25 of the conductive roller 25
The number of sparks and the image quality of output copies were investigated when the rubber material and resistance value of b were varied. The results are shown in the table below.

Condition Vd400V (applied voltage, 1.3KVDc (7)
(b) It is preferable to select urethane rubber rather than silicone rubber from the viewpoint of preventing uneven charging due to oil seepage and from the viewpoint of wear resistance. By using urethane rubber, the relative speed of the conductive roller 25 with respect to the photoreceptor 1 can be increased. This makes it easy to create a difference, which has the effect of reducing charging unevenness due to rotational play of the roller 25, etc., and scraping off minute amounts of corona products adhering to the surface of the photoreceptor due to rubbing.

It has been found that the hardness is preferably 15 to 80 degrees, particularly 45 to 55 degrees, so that the pressure mechanism can be stably set.

It was also found that by increasing the resistance value to 10 5 to 10 6 Ω, it was possible to prevent dielectric breakdown and to obtain high quality images without uneven charging.

d. Applied voltage etc. The voltage applied to the conductive roller 25 may be only DC (direct current), but it may be DC (direct current) with an AC (alternating current) component superimposed on the DC component.
+AC voltage can give better results.

DC component 500~100OV AC component 1200
N1800Hz, soo~reoOv P-P (7
) A good image without charging unevenness was obtained by applying an oc+ac superimposed voltage.

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.

In case of only DC component, 1.0 to 1.5 KV is required.

Although there is an advantage that the incidence of sparks (dielectric breakdown) in the spherical protrusions included in the A-9i photoreceptor is reduced compared to when AC is applied, there is little compensation effect for uneven charging caused by the roller.

The gap precision between the conductive roller 25 and the photoreceptor 1 has a large effect on abnormal discharge due to roller charging. If the conductive roller 25 has backlash or the like, sparks may occur on the upstream side of the contact between the photoreceptor 1 and the roller 25, that is, in the area C in FIG. 1.

Since the voltage of this spark is about 1 to 2 KV, it does not exceed the eI* voltage resistance (OKV) of the A-Si photoreceptor, and therefore it does not immediately cause defects on the photoreceptor.
The image quality may be affected by uneven charging. In order to prevent this from happening, it is also effective to stop the roller 25 from rotating and bring it into pressure contact with the photoreceptor. At this time, it is necessary to select a rubber material for the roller exterior that is resistant to wear, such as urethane rubber. Further, the conductive member 25 need not be of a roller type, but may be a pad member that presses against the surface of the photoreceptor in a non-rotating manner as shown in FIGS. 5(a) and 5(b).

If the photoreceptor is not insulated, a spot (dielectric breakdown) may occur, or even if it does not reach that point, if there are many spherical protrusions, current may flow intensively there, making it impossible to charge the photoreceptor in the axial direction. In order to prevent this, by using a conductive roller with a resistance of 105 or more and using a constant voltage power supply, it has become possible to suppress charge loss in the entire axial direction to a small value of about 2 to 10 mm.

C1. Effects of the Invention As described above, according to the present invention, the surface of a charged body can always be stably and uniformly charged by a contact charging method, and therefore, there are problems as a means for charging a photoreceptor in, for example, an electrophotographic copying machine. In place of a corona discharger which has many advantages, it is possible to realize a practical device equipped with a contact type charging device which has many advantages, and 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 contact-type charging device according to the present invention, FIG. 2 is a perspective view of the charging device with the conductive roller side facing upward, and FIGS. 3 and 4 The figure is a characteristic measurement graph, and FIGS. 5(b) and 5(b) are cross-sectional views of other configuration examples of the conductive member. 1 is a rotating drum type A-9i photoreceptor, 2 is a roller type contact charging device, 25 is a conductive roller, 25a is a shaft rod serving as a metal core thereof, and 25b is a conductive rubber material layer sheathed thereon. 0 12 3 4 5 6 7 8 (KV)
OXX)2X)WataruIB)'1JJED7Q)800':
ω(dacpno@i
Current I1 (Denbe,
Naka 1) Figure 5 (a) (b) Figure 1

Claims (5)

[Claims] (1) A contact charging device that charges the surface of a charged object by bringing a conductive member to which a voltage is applied into contact with the surface of the charged object, the material of at least the surface material of the conductive member that comes into contact with the surface of the charged object. Rubber hardness 15-80 degrees, electrical resistance value 10^
A charging device characterized by being made of a conductive rubber material with a resistance of 5 to 10^6 Ω. (2) The conductive member is a roller body consisting of a metal core and a conductive rubber layer wrapped around it with a rubber hardness of 15 to 80 degrees and an electrical resistance value of 10^5 to 10^6 Ω. The charging device according to claim 1, wherein the charging device is brought into rolling or non-rotating contact with the charging device. (3) The charging device according to claim 1 or 2, wherein the voltage applied to the conductive member is supplied from a power source configured to maintain a constant voltage. (4) The charging device according to claim 3, wherein the voltage applied to the conductive member is a combination of a DC component and an AC component. (5) The charging device according to claim 1, wherein the object to be charged is an amorphous silicon photoreceptor of an electrophotographic apparatus, and the charging device is a device for charging prior to forming a latent image on the surface of the photoreceptor.