JPH0430186A - Contact electrifier - Google Patents

Abstract

PURPOSE:To actually carry out the uniform electrifying processing of a surface to be electrified by arranging a potential uniforming member consisting of a conductive material in such a manner it is brought into contact with a body to be electrified, on the downstream side in the moving direction of the surface of the body compared with the abutting point of a contact electrifying member and the body. CONSTITUTION:The potential uniforming member 10 provided in such a manner that it is brought into contact with the surface of a photosensitive drum 1, on the downstream side in the moving direction of the rotary surface of the photosensitive drum compared with the abutting point of an electrifying roller 2 and the photosensitive drum 1, is a stainless plate in an electrically floating state, and has the dimension of the length of the electrifying roller 2. The potential uniforming member 10 is present thereon so that, even if the surface of the photosensitive drum electrified by the electrifying roller 2 has electrification spots, the peak interval voltages of the electrification spots of the electrified surface to contact with the member 10.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a contact charging device that charges (including neutralizes) the surface of a charged object by bringing a contact charging member to which a voltage is applied into contact with the charged object. It's about improvement.

(Prior Art) For example, in an image forming apparatus such as an electrophotographic device (photographer, laser beam printer, etc.) or an electrostatic recording device, a photoconductor
2. Description of the Related Art Corona discharge devices have been widely used as devices for charging the surface of an image carrier, such as a dielectric material, as a charged object.

A corona discharge device is effective as a means for charging the surface of an object to be charged, such as an image carrier, to a predetermined uniform potential. However, it requires a high-voltage power supply and has problems such as relatively large amounts of undesirable ozone being generated due to corona discharge.

In contrast to such a corona discharge device, a contact charging device, which charges the surface of the charged object by bringing a charging member to which a voltage is applied as described above into contact with the charged object, can reduce the voltage of the power source, and
Since it has the advantage of generating only a very small amount of ozone, it is used, for example, in image forming apparatuses to charge the surface of image carriers such as photoreceptors and dielectrics, and other objects to be charged.
It has attracted attention as an alternative device to corona discharge devices, and research on its practical use is progressing (Japanese Patent Application Laid-Open No. 17826-1983).
7・56-104351・58-40566・58-1
39156.58-] No. 550975).

The present applicant also applied a direct current voltage to a charging member and an oscillating voltage having a peak-to-peak voltage that is more than twice the charging start voltage of the charged object (the voltage value changes periodically over time) for the purpose of stable charging processing, etc. Many proposals have been made, including contact charging methods and devices based on the application of a voltage that changes over time (alternating current components such as sine waves, triangular plates, rectangular waves, pulsating current components) (Japanese Patent Application Laid-Open No. 149668/1983).・Publication No. 149669, etc.).

FIG. 9 shows an example of a contact charging device using a roller type charging member. Reference numeral 1 denotes an object to be charged, which in this example is a photosensitive drum in an electrophotographic apparatus. The photosensitive drum 1 is rotated clockwise as indicated by an arrow at a predetermined process speed (peripheral speed).

Reference numeral 2 denotes a rotating roller body (hereinafter referred to as a charging roller) as a charging member, which has a conductive rubber roller portion 2b formed on the outer periphery of a core metal 2a. They are pressed together with a predetermined pressing force, and in the case of one example, they rotate as a result of the rotation of the photosensitive drum.

Reference numeral 9 denotes a bias applying power source to the charging roller 2, and in this example, a predetermined DC voltage vDc is applied from this power source 9 to the charging roller 2 via the contact plate spring 8 and the roller core metal 28, and the photoreceptor. The surface of the photosensitive drum is charged to a predetermined polarity and potential by applying a superimposed voltage vt, c + vAc with a predetermined oscillating voltage VAC having a peak-to-peak voltage Vpp that is twice or more the charging start voltage. .

Image exposure 3 is then performed on the surface of the photosensitive drum that has been subjected to the charging process to form an electrostatic latent image, and image formation is subsequently performed using a developing device and a transfer device (not shown in the figure). . Reference numeral 6 indicates a cleaning blade as a means for cleaning the surface of the photosensitive drum after transfer.

Reference numeral 13 indicates a charged area on the surface of the photosensitive drum 1 by the charging roller 2, and A indicates its width. Width A is approximately 10μm to 30μm
It is.

The charging member 2 can be of a blade type, a rod type, a block type, etc. in addition to the roller type as described above.

In addition to the rotating drum type as described above, the charged member 1 may be of a rotating belt type, a running wave type, a running sheet type, or the like.

(Problems to be Solved by the Invention) One of the problems with such a contact charging device is as follows.

In contact charging, corona charging occurs, and as mentioned above, the charging area A is very narrow, so it is very susceptible to the influence of the power source 9. Therefore, when charging the surface of the charged object by applying a voltage containing an oscillating voltage component to the charging member, the charging surface of the charged object is charged with a period P corresponding to the oscillating voltage component, as shown in Figure 7. It tends to cause spots. In FIG. 7, the vertical axis represents the surface potential of the charged object charged by the charging member, and the horizontal axis represents the position of the charged object in the plane movement direction. Hereinafter, the charging roller 2, photosensitive drum AC voltage vA will be expressed as the above-mentioned charging member, charged object, and vibration voltage, respectively.
This will be explained as c.

The above-mentioned charge spotting period P is determined as follows.

P=V, /f (1) where vP is the surface movement speed (process speed) of the photosensitive tram 1 as the charged object, and f is the frequency of the AC voltage component of the applied power source 9. Generally, charging spots do not affect images when the surface potential of the photoreceptor is a bright area potential or a dark area potential. However, in the case of halftone potential, the developing bias potential VDev (Figure 7)
As a result, as shown in Fig. 8, a horizontal line P called a cycle ring with period P appears on the output print image.
, will occur. Furthermore, even at the dark potential, if the process speed was too high or the frequency f of the power source 9 was too low, the cycle iP still occurred.

In order to prevent cycle unevenness, there is also a method of increasing the power supply frequency f to make it virtually impossible to develop charging unevenness.

However, there is a limit to this because charging noise (noise generated when the photosensitive drum 1 and charging roller 2 vibrate due to voltage application) becomes more noticeable as the frequency is increased.

When the process speed is high, such as when the image forming apparatus is a high-speed model, it is necessary to increase the frequency of the power supply applied to the charging roller to prevent cycle unevenness, but this frequency is 300Hz.
If it exceeds this, an unpleasant charging sound will generally be produced.

The problems of generation of charging spots, cycle rings, and charging noise are common not only to roller-type charging members but also to ground-type charging members such as blade-type charging members.

■Also, when charging a charged object by applying only a DC voltage component to the charging member, uneven charging may occur due to output voltage fluctuations due to some cause in the output voltage of the DC voltage applying power supply or other causes. may occur. Non-uniform charging causes image unevenness in image forming apparatuses.

The purpose of the present invention is to solve the problems such as (1) and (2) and to enable a contact charging device to carry out a substantially uniform charging process on the surface to be charged. Means) The present invention provides a contact charging device in which a contact charging member to which a voltage is applied is brought into contact with an object to be charged to charge the object. This contact charging device is characterized in that a potential leveling member made of a conductive material is disposed on the downstream side in contact with the object to be charged.

Specifically, the potential leveling member is a conductive member that is electrically suspended (in a floating state), a conductive member to which a DC bias is applied, or the like.

(Function) FIG. 5(A) shows a model diagram of the charge distribution on the surface of the object to be charged, which has charging spots as shown in FIG. 7 described above. That is, on the surface of the charged body 1, there are areas with a large amount of charge e and areas with a small amount of charge e at intervals of a pitch interval P. In this figure, a charged object 1 is an electrophotographic photoreceptor formed by forming a photosensitive layer 1a on the surface of a conductive substrate 1b. The charge e is shown as a negative charge. A positive charge e1 indicates an induced charge generated at the interface between the conductive substrate 1b and the photosensitive layer 1a in response to the charged charge e.

When charging a charged object by applying only a DC voltage component to the charging member, if the surface of the charged object is unevenly charged due to fluctuations in the output voltage, etc., the surface of the charged object is similarly divided into areas where there is a lot of charge e and places where there is little. is created.

The above-mentioned dense and dense state of the charge e on the surface of the charged object works as an insulating surface, so the charge does not move in the direction of the surface of the charged object and is maintained as it is without being leveled. be.

When a conductive member 1o in an electrically floating state or with a DC bias applied is brought into contact with a surface to be charged that has such dense and dense parts as shown in FIG. The charge e can now move in the surface direction of the charged object using the contact conductive member 1o as a conductive path, and the charge density areas on the surface of the charged object are evened out by the movement of the charge.

Therefore, in a contact charging device, a member made of a conductive material is brought into contact with a member made of a conductive material on the downstream side in the surface movement direction of the charged object from the contact portion between the contact charging member to which a voltage is applied and the charged object. Even if charging spots or non-uniformity occur on the charging surface of the charged object charged by the member, the density of the charges is evened out by the charging surface coming into contact with the member, and the charged surface passing through the member position is It will be in a uniform state.

(Example) <Example 1> (FIG. 1) FIG. 1 shows a schematic configuration of an example of an image forming apparatus using a contact charging device according to the present invention.

The image forming apparatus of this example is a laser beam printer (LBP) using a transfer type electrophotographic process.

Reference numeral 1 denotes an electrophotographic photoreceptor as an object to be charged, and the one in this example includes an aluminum drum base 1b and a photoreceptor layer (organic photoconductor (OPC) in this example) 1 formed on the outer peripheral surface of the drum base 1b.
A photosensitive drum with an outer diameter of 30 mm. This photosensitive drum 1 is rotationally driven in the clockwise direction of the arrow at a predetermined process speed vP.

2 is a rotating roller body as a contact charging member similar to the case of the example in FIG.
The conductive roller part 2b is made of PDM, urethane, etc., and is brought into contact with the photosensitive drum 1 with a predetermined pressing force.
By applying a superimposed voltage of a predetermined DC voltage VDC and an AC voltage VAC from 9 through the contact spring plate 8 and the roller core metal 2a, the surface of the photosensitive drum 1 is subjected to a primary charging process to a predetermined polarity and potential ( The dark potential VO) is applied.

Reference numeral 10 denotes a potential leveling member provided in contact with the surface of the photosensitive drum 1 on the downstream side of the contact point between the charging roller 2 and the photosensitive drum 1 in the direction of movement of the rotating surface of the photosensitive drum. The member 10 in this example is an electrically floating stainless steel (SUS) plate having a thickness of 20 μm, and has a length dimension that is approximately the same as the dimension in the drum generatrix direction.

Due to the presence of this potential equalizing member 10, the charging roller 2
Even if charging spots such as those shown in FIG. 7 occur on the charged surface of the photosensitive drum that has been subjected to the charging process, one of the members is then
0 contact, the peak-to-peak voltage of the charging unevenness on the charged surface of the photosensitive drum is reduced to the level shown in FIG. be trained to do so.

Next, a laser image-modulated at a constant printing density D dp+ corresponding to a time-series electric digital pixel signal of target image information is outputted from a laser scanner (not shown) onto the surface of the photosensitive drum whose charged potential has been leveled. By scanning exposure with the light 3, an electrostatic latent image is formed on the surface of the photosensitive drum 1, and toner is supplied to the surface of the latent image from the developing sleeve 4 of the developing means, and the latent image is developed with toner.

On the other hand, a transfer material 7 is fed from a paper feed section (not shown) to a nip portion (transfer section) where the photosensitive drum 1 and a transfer roller 5 as a transfer member come into contact in synchronization with the toner image on the surface of the photosensitive drum 1. Then, the toner image on the first side of the photosensitive drum is sequentially transferred (transferred) to the side of the transfer material 7 by a transfer bias applied to the transfer roller 5 from the power source 15.

The transfer material 7 that has passed through the transfer section is separated from the surface of the photosensitive drum, transferred to a fixing means (not shown), where the image is fixed, and output as an image formed product (print).

After the transfer material has been separated, the surface of the photosensitive drum 1 is cleaned by a cleaning blade 6 to remove adhered contaminants such as residual toner after transfer, and is then turned over and used for image formation.

The primary charging surface of the photosensitive drum 1 by the charging roller 2 (FIG. 7, FIG. 85 (A)) is then charged by the potential leveling member 10 as shown in FIG.
By equalizing the peak-to-peak voltage of charging spots as shown in Figure 5 (B), the dark potential VD will not cross the development bias V DeV level, and the occurrence of cycle spots as shown in Figure 8 can be suppressed. .

<Example 2> (Fig. 2) In this example, the potential leveling member 10A is made of a conductive support plate 10a made of aluminum and conductive carbon fibers 10b are flocked thereto, and the flocked portion 10b is attached to a photosensitive drum. A direct current [12
A bias was applied by .

With this configuration, the surface potential of the photosensitive drum is charged by the charging roller 2 and then equalized by the potential leveling member 10A. Furthermore, the surface potential of the photosensitive drum 1 can be determined to an arbitrary value by the DC bias applied to the leveling member 10A.

In addition, the conductive carbon fiber tab can capture foreign matter such as toner, paper dust, and powder that have slipped through the cleaning blade 6 and the charging roller 2 without damaging the surface of the photosensitive drum 1.

As a result, it has become possible to prevent these foreign substances from moving to the exposed area and blocking the laser beam 3, thereby causing an abnormal image.

<Example 3> (Fig. 3) In this example, a blade type member 2A (charging blade) was used as the charging member, and a conductive thin plate member 10 similar to the one in the example in Fig. 1 was used as the potential leveling member. It was there.

In this case, the area occupied by the charging blade 2A and the potential leveling member 10 is smaller than when the roller 2 is used as a contact charging member, so there is an advantage that parts around the photosensitive drum can be easily arranged.

<Embodiment 4> (FIG. 4) In this embodiment, the potential leveling member is in the form of a rotating roller body 10B. This potential leveling roller IOB is the core metal 1
0c, and a conductive roller portion 10d made of a material such as EPDM-urethane in which carbon is dispersed to reduce resistance. The core bar 10c is electrically floating, and the roller IOB rotates as the photosensitive drum 1 rotates.

When this roller-shaped potential leveling member 10B is used, there are effects such as making it difficult to scrape the surface of the photosensitive drum 1 and preventing the surface of the potential leveling member from getting dirty.

(Effects of the Invention) As described above, according to the present invention, regarding the contact charging device,
The effect of the potential leveling member reduces or substantially reduces the occurrence of charging spots on the charging surface of the charged object due to the oscillating voltage component of the bias potential applied to the contact charging member, and uneven charging on the surface of the charged object due to other causes. Therefore, the surface to be charged can be charged substantially uniformly.

Even in contact charging processing of the charged object surface of a high-speed image forming apparatus, cycle unevenness can be prevented without increasing the frequency of the oscillating voltage component applied to the contact charging member, so charging noise can also be prevented.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an example of an image forming apparatus using a contact charging device according to the present invention. FIGS. 2 to 4 are diagrams of main parts of other embodiments of the apparatus, respectively. FIGS. 5(A) and 5(B) are explanatory diagrams of the potential equalization principle. FIG. 6 is a graph of the charging potential on the surface of the charged object (the dark area potential of the photosensitive drum) after potential equalization. Figure 7 is the same figure as above before potential equalization. Figure 8 is a model diagram of a cycle ring. FIG. 9 is an explanatory diagram of contact charging. 1 is a photosensitive drum as a charged body, 2.2A is a charging roller or charging plate as a contact charging member, 10.IO
A.IOB is a potential leveling member. Illustration (Door 1F - Drum)

Claims (2)

[Claims] (1) In a contact charging device in which a contact charging member to which a voltage is applied is brought into contact with an object to be charged to charge the object, a position downstream of the point of contact between the contact charging member and the object to be charged in the direction of surface movement of the object to be charged. A contact charging device characterized in that a potential leveling member made of a conductive material is placed in contact with a charged object. (2) The contact charging device according to claim 1, wherein the voltage applied to the contact charging member is a voltage including an oscillating voltage component.