JPH04301861A - Contact electrifier - Google Patents

Abstract

PURPOSE:To attain uniform electrification by preventing the occurrence of a noise and unevenness in electrification, in a device impressing a voltage including an ac voltage component to an electrifying member and contact-electrifying a body to be electrified. CONSTITUTION:A second electrifying means 1B is provided so as to be in contact with a photosensitive drum 2 in the down stream side in the photosensitive drum rotating direction of a first electrifying means 1A, at least, impressing an AC voltage Vac on the rotary photosensitive drum (the body to be electrified) 2, to be in contact therewith, and the second electrifying means 1B has the impression of a DC voltage or an electrical floating state. When the frequency of the AC voltage Vac is set at f[Hz], and the revolving peripheral speed of the photosensitive drum 2 is set at P[mm/sec], the contact width L of the second electrifying means 1B to the photosensitive drum 2 is set at >=P/f(mm).

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is a contact charging device that charges (including neutralizes) a charging member to a predetermined potential by bringing a voltage-applied charging member into contact with an object to be charged and moving the two relative to each other. Regarding.

[0002] This device is used, for example, in electrophotographic processes.
In image forming devices such as copying machines, printers, and image display devices that utilize electrostatic recording processes, it is used as a device for charging an image bearing member (charged object) such as a photoreceptor or dielectric material.

0003

BACKGROUND OF THE INVENTION As a contact charging device, the present applicant has previously disclosed in Japanese Patent Laid-Open No. 63-149669, etc., a method in which a voltage (oscillating voltage) in which a DC voltage and an AC voltage are superimposed is applied to a conductive member as a charging member. We have proposed a contact charging device that uniformly charges the surface of a charged object by bringing this conductive member into contact with the charged object.

Charging stability can be obtained by applying a voltage applied to the charging member to a superimposed voltage of DC and AC, and the surface of the charged object can be uniformly charged, and the surface of the charged object can be charged as desired by the value of the DC voltage. Can be done.

FIG. 5 shows an example of this contact charging device, in which a rotating electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) 2 serves as a charging member, and a roller-type conductive member serves as a charging member. sexual member (hereinafter referred to as charging roller)
50 is brought into contact with the charging roller 50, and a voltage (Vac +
By applying Vdc) from the power source 54, the surface of the photosensitive drum 2 can be uniformly charged. The charging potential of the photosensitive drum 2 is determined by the DC voltage, and the AC voltage acts to equalize the charging potential.

The charging roller 50 of this example includes a conductive core metal 51 to which a voltage is applied, and a low resistance layer such as conductive rubber formed concentrically with the core metal into a roller shape by molding or the like. 5
2 and a medium resistance layer 53 made of nylon such as resin formed on the outer periphery thereof, and rotates as the photosensitive drum 2 rotates. When the charging member that is brought into contact with and moves relative to the charged object is a driven rotating roller as in the above example, the relative movement with the charged object is the relative movement between the roller shaft and the charged object. shall be.

[0007]

[Problem to be Solved by the Invention] However, there is a problem called "charging noise" when contact charging is carried out by applying a voltage that is a superimposition of AC voltage and DC voltage to a charging member that is in contact with an object to be charged. This can lead to the generation of harsh vibration noise.

This is because the charging member vibrates due to the applied AC voltage component Vac, and the audibility of this charging sound depends on the frequency of the charging sound, and the frequency of this charging sound depends on the frequency of the applied AC voltage. Depends on frequency. In the apparatus configuration of FIG. 5 described above, the frequency of the AC voltage applied to the charging roller 50 is 40
A harsh charging sound began to be heard at around 0 Hz, and in order to reduce the charging noise to a level that was not bothersome, the frequency of the AC voltage had to be lower than 300 Hz.

The mechanism by which this charging noise occurs will be explained with reference to FIG. The photosensitive drum 2 as an object to be charged has a structure in which a photosensitive layer 2a is provided on the surface of a grounded base layer 2b made of aluminum or the like. Since an alternating current voltage is applied to the charging member 50, at a certain moment, as shown in FIG. A negative charge is induced in Since these charges attract each other, the charging member 5
The surface of 0 is attracted to the photosensitive drum 2 and moves from the position indicated by the solid line to the position indicated by the broken line in the figure.

Next, when the AC electric field starts to reverse, the positive charges on the charging member 50 side and the negative charges on the base layer 2b side of the photosensitive drum 2 begin to be canceled by the induced charges of opposite polarity. Then, when the AC electric field just changes from positive to negative, the positive charges on the charging member 50 and the negative charges on the photosensitive drum base layer 2b disappear. As a result, the surface of the charging member 50 returns to the position shown by the broken line in FIG. 6(B).

[0011] Further, when the AC electric field reaches a negative peak, there is a negative current on the charging member 50 side.
A positive charge is induced on the base layer 2b side of the photosensitive drum 2. Therefore, the charging member 50 moves again from the position shown by the solid line to the position shown by the broken line shown in FIG. 6(C). Since the above phenomenon is repeated, the charging member 5
It is thought that when an alternating current voltage is applied to 0, vibrations begin, and as a result, charging noise is generated.

Assuming that the frequency of the AC voltage is f [Hz] and the vibration frequency of the charging member 50 is F [c/s], as is clear from the above explanation, the charging member 50 changes during one cycle of the AC voltage. will vibrate twice, and there is the following relationship between them.

2f [Hz] = F [c/s] Therefore, if the frequency of the AC voltage applied to the charging member 50 is high, charging noise will become a problem, and if it is too low, the frequency will increase due to the speed of the surface of the charged object. Charging unevenness occurs in pitch. If the frequency of the AC voltage is f [Hz] and the relative movement speed between the charged object and the charging member is P [mm/sec], then the period Z [mm] of the charging unevenness is determined by Z=P. /f. When the period of charging unevenness is larger than approximately 0.2 mm, image quality in the image forming apparatus is degraded. This becomes a problem when trying to increase the printing speed of electrostatic copying machines and printers.

The present invention similarly applies a DC voltage and an AC voltage to a charging member to uniformly contact charge the surface of a charged object, and is a practical contact charging method that eliminates the problems of charging noise and charging unevenness. The purpose is to provide equipment.

[0015]

[Means for Solving the Problems] The present invention is a contact charging device characterized by the following configuration.

(1) A first charging means made of a conductive member that contacts the object to be charged directly or through a resistance layer and moves relative to the object to be charged, and a relationship between the first charging means and the object to be charged. a second charging means made of a conductive member that contacts the object to be charged directly or via a resistance layer on the downstream side of the moving direction, and applying at least an alternating current voltage to the first charging means;
The second charging means applies a DC voltage to it or sets it in an electrically floating state, and sets the frequency of the AC voltage applied to the first charging means to f [Hz] and the relative movement speed of the object to be charged and the charging means. A contact charging device characterized in that, when P [mm/sec], a contact width of the second charging means with respect to the object to be charged in a direction of relative movement with the object to be charged is greater than or equal to P/f [mm]. .

(2) The contact charging device according to (1), wherein the first charging means is a roller-shaped charging member.

(3) The first charging means is a brush charging means in which conductive or medium resistance fibers are arranged in a brush shape, and the second charging means is a brush charging means that is continuous in a direction substantially perpendicular to the direction of relative movement with the object to be charged. The contact charging device according to (1), characterized in that the contact charging means is a blade-like member, a roller-like member, or the like that comes into contact with the object.

(4) (1) characterized in that the frequency of the AC voltage applied to the first charging means is 300 Hz or less
Or the contact charging device described in (2).

[0020]

[Operation] The second charging means is brought into contact with the object to be charged by applying a DC voltage to the downstream side of the object to be charged in the direction of relative movement of the first charging means to the object to be charged. It has the function of leveling and charging the surface of the object to be charged which has been subjected to contact charging treatment.

[0021] Due to the presence of the second charging means, the uniform contact charging performance of the surface to be charged by the first charging means that applies an alternating voltage can be relaxed. In other words, even if the frequency of the AC voltage applied to the first charging means is set to a low frequency that does not substantially generate charging noise, any charging unevenness that may occur due to this is evened out by the second charging means. It is.

[0022] Therefore, it is possible to carry out uniform contact charging without the problems of charging noise and charging unevenness.

[0023]

[Example] <Example 1> (Figures 1 and 2) Figure 1 shows an electronic device in which a photosensitive drum 2 as an image carrier (charged body) is subjected to primary charging using the contact charging device of the present invention. 1 is a schematic configuration diagram of an example of a laser beam printer using a photographic process.

The photosensitive drum 2 moves clockwise as indicated by the arrow at a predetermined circumferential speed P (process speed), which is 94.5 m in this embodiment.
Rotationally driven at m/sec.

1A is a first charging means that is brought into contact with the photosensitive drum 2, and 1B is a second charging means that is brought into contact with the photosensitive drum 2 on the downstream side of the first charging means in the direction of rotation of the photosensitive drum.

The first charging means 1A in this embodiment is a roller body that rotates following the photosensitive drum 2, and has a composite layer structure having a layer structure similar to that of the charging roller 50 shown in FIG. It consists of a metal core 11 to which voltage is applied, a conductive elastic layer 12 made of conductive rubber, etc., and a medium resistance layer 13 made of nylon such as Tresine. The conductive elastic layer 12 has elasticity that allows reliable contact between the roller 1A and the photosensitive drum 2 to be maintained. The medium resistance layer 13 is provided to prevent spark discharge from occurring even if there is a defect such as a pinhole on the photosensitive drum 2.

The first charging means 1A is supplied with a power supply 14, with peak-to-peak pressure Vpp=1.6 kV and frequency f=250.
A voltage Vac+Vdc obtained by superimposing a DC voltage Vdc of minus 750 V on an AC voltage Vac of Hz is applied. The second charging means 1B in this embodiment is a conductive rubber blade body 16 supported on a metal support member 15, and its tip side is brought into contact with the photosensitive drum 2 with a contact width L=0.5 mm. This second charging member 1B was insulated from others and was electrically floated.

The surface of the rotating photosensitive drum 2 is then contact-charged by the first charging means 1A, and then the surface of the rotating photosensitive drum 2 is charged by the second charging means 1A.
B acts to equalize the charged potential.

In this case, the surface potential of the photosensitive drum after being charged by the first charging means 1A was about -700 V, and since the frequency of the applied AC voltage was lowered, charging unevenness occurred with a period of about 0.4 mm.

However, this charging unevenness is eliminated by averaging in units of 0.5 mm using a conductive rubber blade having a contact width L=0.5 mm as the second charging means 1B.

That is, the second charging means 1B is the first charging means 1A.
It has a leveling effect that averages out the uneven charging of the photosensitive drum surface potential caused by the low frequency of the AC bias.

The contact width L of the second charging means 1B with respect to the photosensitive drum 2 has a length equal to or longer than one cycle of charging unevenness (L0 in FIG. 2, in this example, L0=94.5/250=0.378 mm). Although necessary, it is desirable that the length be at least twice that length.

In the present embodiment, the second charging means B is insulated from others and placed in a floating state, but uniformity of charging can be further improved by applying -700 V as a DC bias.

Image information is scanned and exposed by the laser beam 5 to the two surfaces of the photosensitive drum which have been subjected to the primary charging process as described above, toner development is performed by the developing device 6, and the formed toner image is transferred onto the transfer material 7 by the transfer roller 8. The steps are executed, and the transfer material 7 separated from the surface of the photosensitive drum 2 after the toner image transfer is introduced into a fixing device (not shown) and output as an image formed product (print). After the toner image has been transferred, the surface of the photosensitive drum is cleaned by a cleaning device 9 to remove contaminants such as residual toner, and is used repeatedly for image formation.

Note that in this embodiment, the first charging means is a charging roller that rotates driven by the photosensitive drum, but it is not limited to driven rotation, but can be driven rotation, and the circumferential speed of the photosensitive drum and the charging roller are set to different values. Needless to say, it's a good thing. Also in this case, the relative moving speed in the present invention means the relative moving speed between the first charging means and the surface of the photosensitive drum,
It is 94.5 mm/sec, and is not related to driven rotation or drive rotation. The key is to equalize the charging unevenness that occurs during the first charging by making the contact width between the second charging means and the object to be charged longer than one period of the charging unevenness, and the period of the charging unevenness is determined by the charging voltage. It is determined only by the frequency and the moving speed (absolute speed) of the object to be charged, and is unrelated to the rotation speed, rotation speed, and running speed of the first charging means such as a roller body.

Example 2 (FIG. 3) In this example, in the charging device of Example 1, the second charging means 1B is also a roller body that rotates following the photosensitive drum 2, similar to the first charging means 1A. By using a roller type as the second charging means 1B as in this embodiment, in which a DC bias is applied from a DC power supply 17 to the second charging means 1B, the contact width L with the photosensitive drum 2 can be increased. , it is compatible with higher speed image forming apparatuses. Therefore, the outer diameter of the roller body serving as the second charging means 1B is set to 20 mm, the diameter of the metal core 11 is set to 10 mm, and the roller body is
When pressed against the photosensitive drum 2 with a spring pressure of g, the nip (=
The contact width L) was approximately 2.5 mm. As a result, even if the frequency of the AC bias applied to the first charging means 1A is 100 Hz, it is applicable to an image forming apparatus with a process speed of up to P=250 mm/sec.

Embodiment 3 (FIG. 4) In this embodiment, the first charging means 1A is a brush body, and a plurality of second charging means 1B are sequentially arranged in the rotational direction of the photosensitive drum 2. It has two blade bodies.

The brush body as the first charging means 1A is a medium resistance brush 1 made of nylon or the like on a conductive support 18.
9 is provided, and the brush 19 is brought into contact with the photosensitive drum 2. An AC/DC superimposed voltage Vac+Vdc is applied to the conductive support 18 from the power source 14.

The two blade members serving as the second charging means 1B each consist of a metal support 15 and a conductive rubber blade 16, similar to the blade members serving as the second charging means 1B shown in FIG. Metal support 15
・16 Both blade members are electrically connected to have the same potential, and both blade members are electrically insulated from each other to be in a floating state.

With the above configuration, charging unevenness caused by the frequency of the AC bias component applied to the first charging means 1A can be more reliably removed. Furthermore, since the two blade members serving as the second charging means 1B are in continuous contact with the photosensitive drum 2 in the lateral direction, this has the effect of making the lateral charging uniform, and the brush charging of the first charging means 1A is effective. This second charging means 1B can also remove partial charging defects that result in vertical striped images that are likely to occur. In this embodiment, the second charging means 1B is insulated from others and is in a floating state, but applying a DC voltage is more effective in making charging uniform.

[0041]

[Effects of the Invention] As described above, according to the present invention, the problems of charging noise and charging unevenness that occur when contact charging the surface of a charged object by applying a DC voltage and an AC voltage to a charging member can be solved with a simple structure. It can be resolved.

[Brief explanation of drawings]

[Figure 1] Schematic configuration diagram of the first embodiment device

[Figure 2]
Periodic diagram of charging unevenness

[Figure 3] Main part diagram of the second embodiment device

[Figure 4] Main part diagram of the third embodiment device

[Figure 5] Schematic diagram of a conventional device example

[Figure 6] (A), (B), and (C) are illustrations of charging sound generation, respectively.

[Explanation of symbols]

1A First charging means 1B Second charging means 2 Photosensitive drums 14 and 54 as objects to be charged
Power source L Contact width of the second charging means with the charged object in the rotating direction of the charged object

Claims (4)

[Claims] 1. A first charging means made of a conductive member that moves relative to the charged object by contacting the charged object directly or through a resistance layer, and relative movement of the first charging means with the charged object. a second charging means made of a conductive member that contacts the object to be charged directly or via a resistance layer on the downstream side of the direction;
At least an alternating current voltage is applied to the first charging means, and the second charging means applies a direct current voltage or makes it electrically floating, and the frequency of the alternating current voltage applied to the first charging means is f[ Hz], and the relative moving speed between the charged object and the charging means is P [mm/sec], and the contact width of the second charging means with respect to the charged object in the direction of relative movement with the charged object is P/sec. A contact charging device characterized in that it is f [mm] or more. 2. The contact charging device according to claim 1, wherein the first charging means is a roller-shaped charging member. 3. The first charging means is a brush charging means in which conductive or medium resistance fibers are arranged in a brush shape, and the second charging means is a brush charging means in which conductive or medium-resistance fibers are arranged in a brush shape, and the second charging means is a brush charging means in which conductive or medium resistance fibers are arranged continuously in a direction substantially perpendicular to the direction of relative movement with the object to be charged. 2. The contact charging device according to claim 1, wherein the contact charging means is a blade-like member, a roller-like member, or the like that comes into contact with the contact charging device. 4. Claim 1, characterized in that the frequency of the AC voltage applied to the first charging means is 300 Hz or less.
Or the contact charging device described in 2 above.