JPH0659557A - Electrostatic charging device - Google Patents

Abstract

PURPOSE:To provide the electrostatic charging device for image formation which is simple in the construction of a charge imparting member and can maintain always stable electrostatic charge. CONSTITUTION:A conductive fiber assemblage 51 is used as the charge imparting member to be brought into contact with a photosensitive body 1 forming an electrostatic latent image. This fiber assemblage 51 is constituted of >=2 kinds of the conductive fiber materials varying in resistance value from each other and vibrating electric fields are formed on the surface of the photosensitive body 1 by the relative movement of the conductive fiber assemblage 51 and the photosensitive body 1. The quantity of the charges to be implanted from the conductive fibers to the photosensitive body 1 is decreased, by which the sweeping seam-like unequal electrostatic charge on the photosensitive body 1 is eliminated and eventually the desired purpose is attained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for charging a photoconductor (photoconductive dielectric layer) of an image forming apparatus.

[0002]

2. Description of the Related Art As a device for charging a photosensitive member of an image forming apparatus to a desired potential, a corona charger using corona discharge has been conventionally used. However, since the corona charger needs a high voltage, there is a possibility that the corona charger often has an electrical influence on the microcomputer,
Furthermore, since a large amount of ozone is generated during corona discharge,
In addition to problems on the device such as deterioration of the photoconductor and parts inside the device, especially resin parts such as cleaning blades,
There are also environmental problems such as the discomfort to the users caused by the generated ozone, and in order to eliminate these points, conventionally,
A charging method by contact has been proposed.

In this charging method using contact, charging occurs due to discharge in a gap near the contact point of the charging member, and the discharge current flows through the charging member. For this reason, it is desirable that the charging member has a low resistance in order to reduce the influence of the voltage effect. In consideration of this point, the charging member conventionally has a shape as shown in FIG. 8 (a). Conductive rubber roller 805 is used.

[0004]

By the way, according to the charging device adopting the above-mentioned contact method, it is necessary to form the conductive rubber roller with a material which does not change with time, and in order to obtain a uniform discharge. , It is necessary to finish the roller surface extremely smoothly. Further, even if an abnormal current flows through the conductive rubber roller due to a pinhole or the like existing on the photoconductor, the roller should not be damaged, and the conductive rubber roller as a whole should not have a voltage drop. There is a problem that various conditions in manufacturing are strict, such as that it is necessary to do it.

Therefore, in order to solve such a problem, a device for charging by using a conductive fiber assembly as a charge imparting member and applying a voltage while the fiber assembly is in contact with a photoreceptor. Is proposed. As the charging contact method, for example, a method of contacting the conductive fibers and the photoconductor 801 with the plate-shaped conductive fiber assembly 851 as shown in FIG. 8B fixedly held, Although not shown, there is a method in which a conductive fiber assembly is wound around a conductive core member to form a brush roller structure, and the conductive fiber and the photoconductor are brought into contact with each other while rotating the roller.

However, the former one of these methods has the advantage that the apparatus is simple in structure, but foreign matter such as toner is likely to accumulate on the conductive fibers, which results in image quality deterioration due to uneven charging. There is a problem that it tends to decrease. On the other hand, according to the latter method, since the conductive fiber aggregate moves with respect to the photoconductor, it is difficult for foreign matter to accumulate. Furthermore, cleaning means for foreign matter can be attached. Still, it is not possible to completely remove the mesh-shaped charging unevenness of the fiber.

The present invention has been made in view of the above circumstances, and an object of the present invention is to adopt a conductive fiber assembly having a relatively simple structure as a charge imparting member, which is always stable. An object of the present invention is to provide a charging device capable of sustaining the electrostatic charge.

[0008]

A structure for achieving the above object will be described with reference to FIG. 1 corresponding to an embodiment. The present invention will be described below with reference to a photoreceptor 1 for forming an electrostatic latent image. In the apparatus for charging the photoconductor 1 by bringing the conductive fiber assembly 51 into contact with the conductive fiber assembly 51 and applying a voltage to the fiber assembly 51, the conductive fiber assembly 51 is provided with at least 2 different resistance values. The conductive fiber materials 51H and 51L are composed of more than one kind, and the conductive fiber materials 51H and 51L are sequentially positioned at a predetermined cycle at the portion where the conductive fiber aggregate 51 of the photoconductor 1 contacts. It is characterized by the provision of transportation means for moving it.

As the above-mentioned moving means, for example,
The charging member has a brush roller structure in which two kinds of conductive fiber materials 51H and 51L of high resistance and low resistance are wound in two spirals, and the rotation of the roller causes the same portion on the surface of the photoconductor 1 to rotate. Both high and low fiber materials are alternately located in the.

[0010]

First, the charging mechanism of the photosensitive member by the conductive fiber aggregate composed of a single conductive fiber material is considered as follows.

The conductive fiber and the photosensitive member are given relative rotational motion in a state of being in contact with each other, and in this state,
For example, a part where the conductive fiber and the photoconductor are in contact with each other, such as a leading edge portion of the conductive fiber, and a part having a certain distance from the photoconductor, such as the vicinity of the contact part or a side surface of the conductive fiber, are provided. it can. Here, when a voltage is applied to the air gap in such a close portion, discharge occurs according to the discharge characteristic (example) of Paschen shown in FIG. Due to this discharge, electric charges move to the side of the photoconductor, and when the potential of the void becomes equal to or lower than the discharge start voltage, the discharge stops.

On the other hand, at the contact portion between the conductive fiber and the photosensitive member, the charge moves from the side having a higher potential to the side having a lower potential. Although the fiber contact portion is relatively wide, it is considered that the charging due to the discharge has already been completed in the region on the upstream side of the fiber contact portion.
Therefore, even after charging by discharge, there is a potential difference of several hundreds of volts between the leading edge of the conductive fiber and the photoconductor, and the electric charge is continuously injected into the contact portion of the fiber with the photoconductor.
This charge injection raises the surface potential of the photoconductor. Therefore, the potential is high at the part where the contact time of the conductive fiber is long or the part where the contact probability is high, which causes the sweeping of the conductive fiber to appear as uneven charging.

Therefore, in the present invention, a conductive fiber assembly is formed of two or more kinds of conductive fiber materials having different resistance values, and the fiber assembly is moved relative to the photosensitive member. By forming an oscillating electric field at the same portion (a portion along the circumferential direction of rotation) on the surface of the photoconductor, increase in surface potential due to charge injection at the fiber contact portion is suppressed. That is, by oscillating the electric field on the surface of the photoconductor, immediately after the charging by discharge is completed, the potential difference between the tip edge of the conductive fiber that contacts the charged part and the photoconductor is reduced, and the electric field from the fiber is reduced. The amount of charge injection into the photoconductor is reduced.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. First, a schematic structure of an image forming apparatus to which the present invention is applied will be described with reference to FIG.

Image data relating to image formation sent from a host computer (not shown) is the controller 1.
6 is processed. Following this, an image formation start signal is sent to the engine controller 17, and from this time point, each unit is operated in accordance with the previously input process.

The specific operation of each step is as follows. First, the transfer material (eg, paper) stored in the transfer material cassette 7 is
The sheet is pulled out one by one by the sheet feeding roller 8 and is conveyed to a position before the registration roller 11 by the conveying rollers 9 and 10.

On the other hand, the surface of the photosensitive member 1 is uniformly charged at a predetermined potential by a charging roller 5 having a structure described later. The photoconductor 1 is rotated clockwise in the drawing at a constant speed by a rotation drive mechanism (not shown).

Further, in the developing device 2, the toner is supplied from the toner tank 2e to the supply roller 2b and the developing tank 2f so that the toner on the magnet roller 2d has a predetermined density.
To the mixer roller 2c and agitated by the mixer roller 2c. At this time, the toner is charged to the same polarity as the charging potential of the photoconductor 1, and therefore the toner is exposed on the surface of the photoconductor by applying a voltage close to the charging potential of the photoconductor 1 to the magnet roller 2d. The writing head 6 adheres to a portion irradiated and is developed.

Then, the transfer material conveyed to the front of the registration roller 11 is transferred by the registration roller 11.
It is sent to the transfer roller 3 at a timing corresponding to the image position of the photoconductor 1. At this time, a voltage having a polarity opposite to that of the toner is applied to the transfer roller 3, whereby the toner on the surface of the photoconductor 1 is transferred to the transfer material. The transfer material after the toner transfer is sent by being sandwiched between the heat roller 12a and the pressure roller 12b of the fixing device 12, and the toner is melted and fixed on the transfer material while passing through the two rollers 12a and 12b. To be done. After that, the transfer material is sent to the stack guide 15 by the transport roller 13 and the paper discharge roller 14. On the other hand, in the previous transfer, the toner not transferred from the photoconductor 1 is scraped off from the surface of the photoconductor 1 by the cleaning blade 4a of the cleaning unit 4, and the toner screw 4b is used to dispose the toner (not shown). Is discharged to.
This completes the series of image forming steps.

Now, the charging roller 5 used in the embodiment of the present invention.
As shown in FIG. 2 (a), the conductive charging roller shaft 53 having a diameter of 6 mm is attached to the enlarged view of FIG. 2 (b) [B in FIG. 2 (a)].
Part], the conductive fiber cloth 51 having the structure shown in FIG.

The conductive fiber cloth 51 is composed of a fiber bundle row 51H having a high resistance value in which the carbon content of the carbon dispersed rayon is adjusted, and a fiber bundle row 51L having a lower resistance value. 0.5mm on each 20mm wide cloth
The structure is arranged alternately at intervals. Further, the conductive fiber cloth 51 is wound around the charging roller shaft 53, and thereafter, the ends of the fibers are cut so that the outer diameter of the whole is 12 mm. The resistance values of the fiber bundle rows 51H and 51L are set to high and low by adjusting the amount of carbon dispersion.

The charging roller 5 having the above-described structure is supported by a gap holding material (not shown), and the conductive fiber cloth 51 of the charging roller 5 bites into the outer peripheral surface of the photoreceptor 1 shown in FIG. With the roller driving motor 52 at a speed 20 times the peripheral speed of the photoconductor 1
Is rotated in the opposite direction.

Next, the operation of the embodiment of the present invention will be described with reference to FIGS. First, focusing on one point of the contact position between the photoconductor 1 and the charging roller 5 which rotate in opposite directions, for example, the point A shown in FIG.
As shown in (a), the fiber bundle row of the charging roller (low resistance)
When 51L is located, a high electric field is applied between the photoconductor 1 and the charging roller 5 at the point A. On the other hand, as shown in FIG. 9B, when the fiber bundle row (high resistance) 51H of the charging roller is located on the point A, a low electric field is applied between the photoconductor 1 and the charging roller 5. To be done.

The conductive fiber cloth 51 in which the respective fiber bundle rows 51H and 51L are alternately arranged is wound around the roller in a spiral shape, and the charging roller 5 rotates at a constant speed. On the point A, the low resistance conductive fiber material and the high resistance conductive fiber material are alternately located at a constant cycle, which results in the point A shown in FIG.
As shown in (c), an oscillating electric field in which a high electric field [(b) state] and a low electric field [(b) state] are periodically applied is formed. Although the above description has been made only for the point A, it is needless to say that the oscillating electric field is also formed in other parts by the same action.

In the embodiment having the above structure, a DC voltage was applied to the charging roller 5 to form an oscillating electric field between the photoconductor 1 and the conductive fiber aggregate 51. No unevenness occurred. here,
The oscillating electric field is determined by the resistance of the two kinds of conductive fiber materials and the mixing ratio and density thereof. For the low resistance conductive fiber material, the resistance value is set so that charges are not back-injected from the photoconductor to the fiber material. Further, it is preferable to set the resistance value of the conductive fiber material having high resistance to a dischargeable value. In this example, the charging roller 5 is provided with -1200V.
Is applied, and the surface of the photoconductor 1 is uniformly charged to a desired potential (−600 V).

The present invention is not limited to the configuration of the above embodiment and can be implemented by adopting other alternative means. For example, as shown in FIG. 5, a high resistance fiber bundle row 151 of conductive fiber cloth 151 provided on the outer periphery of the charging roller 105.
It is also possible to adopt a structure in which H and the low resistance fiber bundle row 151L are arranged so as to be parallel to the rotation axis direction of the charging roller 105 and the charging roller 105 is rotated by the motor 152. As shown in FIG. 6, the high resistance fiber bundle row 251H and the low resistance fiber bundle row 251L of the conductive fiber cloth 251 are arranged so as to be orthogonal to the rotation axis direction of the charging roller 205, and the charging roller 205 is
You may employ the structure which vibrates along the axial direction.
Alternatively, as shown in FIG. 7, the electrically conductive fiber cloth 351 provided on the outer periphery of the charging roller 305 has a structure in which rectangular high resistance fiber bundle rows 351H and low resistance fiber bundle rows 351L are randomly arranged. It may be configured to give rotation or vibration in the axial direction. 5 to 7, FIG. 5 (b) is a partially enlarged view of the conductive fiber assembly 151 ... 351 of FIG. 5 (a).

Further, in the above embodiments, the charging roller driving means may be a mechanism using a dedicated motor as a driving source as shown in FIG. 2 or the like, or for driving a photoconductor or the like. A mechanism using the power source of may be adopted.

Further, in the above-described embodiments of the present invention, the structure of the charging member is a brush roller, but the present invention is not limited to this, and two or more kinds of conductive fiber cloths having different resistance values are formed into a belt shape. You may use the thing of the structure wound around. Even in this case, in order to form an oscillating electric field on the surface of the photoconductor, the belt-shaped conductive fiber cloth is moved relative to the photoconductor to obtain the same effect as that of the roller. I'm dying.

Furthermore, in the present invention, there is no particular problem even if the conductive fiber aggregate is made of three or more kinds of conductive fiber materials having different resistance values.

[0030]

As described above, according to the present invention,
The conductive fiber assembly that is brought into contact with the photosensitive member that forms the electrostatic latent image is made up of two or more kinds of conductive fiber materials having different resistance values, and the conductive fiber assembly and the photosensitive member are relative to each other. Since it is configured to form an oscillating electric field on the surface of the photoconductor by such a movement, the amount of charges injected from the conductive fibers to the photoconductor is reduced, and as a result, the photoconductor does not have sweep-like charging unevenness. It is possible to obtain high-quality images. Moreover, the above effects can be achieved with a relatively simple device configuration.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of an image forming apparatus to which the present invention is applied.

FIG. 2 is a diagram showing a structure of a charging roller 5 of an embodiment of a charging device of the present invention.

FIG. 3 is an explanatory view of the operation of the embodiment of the present invention.

FIG. 4 is an explanatory view of the operation of the embodiment of the present invention.

FIG. 5 is a diagram showing the structure of another embodiment of the present invention.

FIG. 6 is a diagram showing the structure of another embodiment of the present invention.

FIG. 7 is a diagram showing the structure of another embodiment of the present invention.

FIG. 8 is a diagram showing an example of a conventional structure of a charging member.

FIG. 9 is a graph showing an example of Paschen's discharge characteristics.

[Explanation of symbols]

 1 ... Photoreceptor 5 ... Charging roller 51 ... Conductive fiber cloth (conductive fiber aggregate) 51H ... Conductive fiber material (high resistance) 51L ... Fiber material (low resistance) 52 ... Roller drive motor 53 ... Charging roller shaft

Claims (1)

[Claims] 1. An apparatus for charging a photoreceptor by contacting a conductive fiber assembly with a photoreceptor for forming an electrostatic latent image, and applying a voltage to the fiber assembly to charge the photoreceptor. The conductive fiber aggregate is composed of at least two types of conductive fiber materials having different resistance values from each other, and the plurality of types of conductive fibers are provided at a portion of the photoreceptor where the conductive aggregate contacts. A charging device comprising means for sequentially positioning each of the materials in a predetermined cycle.