JPH07101324B2 - Contact charging device - Google Patents

Description

The present invention relates to a contact charging device, and in particular, an oscillating voltage is applied to a charging member to charge an object to be charged such as an electrophotographic photosensitive member to a predetermined voltage (including static elimination). ) Related to the contact charging device.

[Conventional technology]

Recently, a contact charging method has been proposed in which a voltage is applied to a conductive member (charging member) from the outside and the charging member is brought into contact with a member to be charged such as an electrophotographic photoreceptor to perform charging. In comparison with the conventional corona charging method, there are advantages that a lower applied voltage can be used, less ozone is generated, and the like.

Conventionally, such a contact charging device has a problem that uneven charging occurs as compared with charging by a corona discharger, but the applicant of the present invention has disclosed that the contact charging member and the member to be charged are different from each other in JP-A-63-149669. This was solved by forming an oscillating electric field in the.

According to this contact charging method, for example, as shown in FIG. 10, the charging roller 1 which is a charging member is contact-rotated with the electrophotographic photosensitive drum 2 and has a peak-to-peak voltage Vpp which is more than twice the charging start voltage. By applying a voltage (Vac + Vdc) obtained by superimposing the AC voltage Vac and the DC voltage Vdc to the core metal 1a of the charging roller 1 from the power supply 3 through the contact 4, the photosensitive drum 2 can be uniformly charged. The charging roller 1 is pressed against the photosensitive drum 2 by a spring 5.

[Problems that the invention is trying to solve]

As a result of the research and experiment by the present inventors, the charging roller 1 as described above is used.
When the contact charging is performed by using, the conductive elastic member 1b vibrates due to the AC component Vac of the voltage applied to the core metal 1a, and the nip portion between the charging roller 1 and the photosensitive drum 2 It was found that a vibrating sound that is charged at the contact part) is generated.

Fig. 11 shows the mechanism of vibration noise generated by this charging.
This will be described with reference to the enlarged view of the nip portion between the charging roller 1 and the photosensitive drum 2 shown in FIG.

In the figure, 2a is a photosensitive layer, and 2b is a base layer made of aluminum and is grounded. Since an AC voltage is applied to the charging roller, at a certain moment, as shown by the broken line in the figure, a negative charge is placed on the charging roller side across the photosensitive layer 2a and a positive charge is placed on the aluminum layer side of the photosensitive drum. Is induced. Since these charges attract each other, the surface of the charging roller is also attracted to the photosensitive drum. Then, when the electrolysis reverses, the charges move so as to cancel the positive and negative charges, respectively, as shown by the solid line in the figure. As a result, the attracted charges are reduced, and the charging roller returns to a position where the force of pressing the charging roller 1 against the photosensitive drum 2 by the spring 5 and the elastic force due to the compressive deformation of the charging roller 1b are balanced. Further, when positive charges are induced on the charging roller side and negative charges are induced on the photosensitive drum substrate side, a pulling force is generated again.

Since the above phenomenon occurs repeatedly, it is considered that the charging roller vibrates when an AC voltage is applied to the charging roller.

When the charging roller vibrates in this way, air movement occurs at that portion as shown in FIG. When the charging roller 1 attracts the photoconductor drum 2, the air moves in the direction of the broken line arrow in the figure, and when the attractive force disappears, the air moves in the direction of the solid line arrow in the figure. At this time, the air in the irregularities (A in the figure) on the surface of the charging roller 1 in the figure is discharged to the outside from the position B, which is very narrow when the charging roller comes to the position of the broken line.
Similarly, when the charging roller returns to the solid line, the air similarly passes through the portion B and moves in the direction of the solid arrow in the figure. Therefore, since the air moves in the narrow portion B, a vibration noise is generated when an AC voltage is applied to the charging roller.

Further, it was found that if the AC component Vac of the applied voltage is eliminated, no sound is generated, but uniform charging of the surface of the photoconductor drum 2 cannot be obtained, and spot-like charging unevenness occurs. It is considered that this is because both surfaces of the charging member 1 to which a voltage is applied and the photosensitive drum 2 in contact with the charging member 1 are microscopically uneven, and it is difficult to obtain an ideal contact surface. Furthermore, even if a normal electrophotographic image forming process is applied to the surface of the photosensitive drum in the spot-like uneven charging state, the output image becomes a spot-like black spot image corresponding to the spot-like uneven charging, and a high-quality image cannot be obtained. Can not.

In order to solve the above problem, a method has been proposed in which an anti-vibration agent layer such as rubber is formed inside the photoconductor drum 2, that is, between the conductive substrate 2b and the photoconductor layer 2a, and the AC component Vac is applied. However, it is not practical in terms of deformation, weight and manufacturing cost of the photosensitive drum.

On the other hand, when the charging member is brought into contact with the photosensitive drum to be charged as described above, the photosensitive drum is scraped due to abrasion with the charging member, so that the charged electric charge may not be properly transferred to the photosensitive drum.

[Object of the Invention]

The present invention has been made in view of the above problems, and reduces vibration noise generated between a contact charging member and a member to be charged, and prevents scraping due to wear of the member to be charged. An object of the present invention is to provide a charging device that uniformly charges a body.

[Structure of Invention]

In order to achieve the above-mentioned object, the present invention is a contact charging device for charging by charging a charging member to which an oscillating voltage is applied to a member to be charged, and the ten-point average surface roughness Rz of the charging member is 5
It is characterized in that it is larger than μm and smaller than 100 μm.

〔Example〕

Next, the contact charging device according to the present invention will be described in more detail with reference to the drawings.

FIG. 1) shows an embodiment of the contact charging device according to the present invention. In this embodiment, the member to be charged is the electrophotographic photosensitive drum 2
The photosensitive drum 2 comprises a drum base body 2b made of aluminum, a photosensitive body layer formed on the outer peripheral surface of the base body 2b, and an organic photoconductor (OPC) 2a in this embodiment. The photosensitive drum 2 has an outer diameter of 30 mm in this embodiment, and is indicated by an arrow A
Is rotated at a predetermined speed. The photosensitive drum 2 is charged by the contact charging device according to the present invention.

As shown in FIG. 13, after the photoconductor is uniformly charged by the contact charging device, an electrostatic latent image is formed by irradiating the charged surface with the light image 7 by the reflected light of the original or the laser light which is image-modulated. Then, toner is supplied from the developing device 8 to the latent image to form a toner image. The transfer roller 10 is in pressure contact with the downstream side of the developing device in the rotational direction A of the photoconductor 2, and a transfer material (not shown) supplied from the transport path 9 is timed with the toner image on the photoconductor surface. The toner is transferred to the pressure contact portion between the photoconductor 2 and the transfer roller 10. At this time, a transfer bias is applied to the transfer roller 10 from the power source 3, and the toner image is transferred from the photoconductor to the transfer material. After that, the transfer material having the adhesive toner image is separated and discharged to the outside of the apparatus through a fixing portion (not shown). Also, the toner remaining on the photoconductor after transfer is cleaned by a cleaning device.
It is cleaned by 11.

As shown in FIG. 1, the contact device according to the present invention includes a charging member that comes into contact with the photosensitive drum 2 with a predetermined pressure, that is, a roller-shaped charging roller 1 in the present embodiment, and the photosensitive drum 2 rotates. Along with that, it rotates following the arrow. Here, the charging roller 1 may be driven and rotated in the same direction or in the opposite direction at the contact portion with the photosensitive drum 2. However, in order to prevent abrasion due to wear of the charging roller 1 and the photosensitive drum 2, the charging roller 1 is driven to rotate with respect to the photosensitive drum 2, or the charging roller 1 is driven to rotate in the same direction at the contact portion at the same speed. It is desirable to let Charging roller 1
Has a metal cored bar 1a and a conductive elastic layer 1b formed on the outer periphery of the cored bar, and has an outer diameter of 12 mm (diameter 6 m of the cored bar 1a.
m, the thickness of the conductive elastic layer 1b was 3 mm, and the ten-point average roughness Rz of the surface was 30 μm. Here, the ten-point average roughness Rz of the surface of the charging member was measured by a universal surface profilometer SE-3C of Kosaka Laboratory based on JIS standard number JIS-B-0601.
A voltage is applied to the charging roller 1 from the power supply unit 3, and an oscillating voltage (Vac + Vbc) in which the AC voltage Vac and the DC voltage Vdc are superimposed
Is supplied to the core metal 1a. Here, the oscillating voltage is a voltage whose voltage value periodically changes with time. More specifically, preferably, the charging member, that is, the charging roller 1, is applied with a voltage (Vac + Vdc) obtained by superposing the AC voltage Vac and the DC voltage Vdc, which have a peak-to-peak voltage Vpp that is at least twice the charging start voltage. . Moreover, the waveform of the oscillating voltage is not limited to the sine wave, and may be a rectangular wave, a triangular wave, or a pulse wave.

The conductive elastic layer 1b is formed of elastic rubber such as EPDM and NBR,
The surface of the mold is polished or the mold is provided with recesses to allow the projections 1c to be formed beforehand, so that the average roughness is sufficiently 30 μm.
It is built to a certain degree.

FIG. 1) is a perspective view of the charging roller 1. At this time, the hardness of the charging roller was ASKER-C60 °.

With the above configuration, the photosensitive drum 2 is rotated at a peripheral speed of 20 mm / sec, and the charging roller 1 is supplied with a DC voltage Vd of −700 V from the power supply unit 3.
c, peak-to-peak voltage 1500V, frequency 1000Hz AC voltage Vac
Then, the photosensitive drum 2 was uniformly charged to about -700V.

Moreover, the sound generated by the vibration of the charging roller 1 and the photoconductor drum 2 can fall below 50 dB when the ten-point average roughness Rz on the surface of the charging roller 1 is larger than 5 μm, as shown in FIG. 1). There was no problem in practice. Further, if Rz is set to 30 μm or more, the vibration noise is less than 30 dB, which is more preferable.

However, it has been found that when Rz is 100 μm or more, the phenomenon in which the charging roller 1 scrapes the surface of the photosensitive drum 2 becomes conspicuous.

This is shown in the graph of FIG. 1). The horizontal axis represents the ten-point roughness average Rz on the surface of the charging roller 1, and the vertical axis represents the scraped amount of the photosensitive drum 2 (OPC: organic photosensitive member) after endurance.

As a result, the ten-point roughness average of the charging roller 1 surface is 100 μm.
It can be said that the surface of the photoconductor is apt to be sharply ablated in the above cases.

The reason for this is considered as follows. That is, the ten-point roughness average Rz on the surface of the charging roller 1 is
When the thickness is 100 μm or more, the pressure applied to one minute protrusion on the surface of the charging roller 1 increases as Rz decreases, if the pressing pressure of the charging roller 1 is constant.

As a result, the pressure is increased and the surface of the photoconductor is easily scraped due to wear at the raised portion. Therefore, Rz is larger than 5 μm and smaller than 100 μm.

The reason why the vibration noise is reduced by roughening the surface of the charging roller 1 will be described with reference to FIG.

In the figure, 1C is a protrusion on the surface of the charging roller 1. When the charging roller and the photoconductor drum are attracted to each other (broken line in the figure), the protrusion interferes with the adhesion between the charging roller 1 and the photoconductor drum 2. Then, the air moving in the direction of the dashed arrow in the figure can pass around 1C relatively easily. As a result, the vibration noise generated at this time is also reduced.
Similarly, when the air in the direction of the solid arrow in the figure moves, the movement of the air becomes easier due to the presence of 1C, and the vibration noise also decreases.

This phenomenon is similar to the fact that claps with gloves are quieter than claps with bare hands.

3 to 9 show another embodiment of the contact charging device of the present invention.

In FIG. 3, a groove having a depth of 50 μm (10-point average roughness 50 μm) and a pitch of 10 μm is formed on the surface of the conductive layer 1b in the same direction. In this case, even if the charging roller 1 vibrates due to the application of the AC voltage, the air in the portion in contact with the photosensitive drum 1 can move smoothly. Therefore, the vibration noise is reduced.

Moreover, as shown in FIG. 4, a width of 10 μm is formed on the surface of the conductive layer 1b.
Even if a m-long, 50-μm long, 30-μm high (10-point average roughness of 30 μm) protrusion was formed by molding, the same sound countermeasure effect was obtained.

Further, as shown in FIG. 5, the conductive layer 1e has a skin layer formed on sponge-like foamed carbon-containing EPDM, NBR, etc., and has a 10-point average roughness of 50 μm on the surface thereof.
It may be one with a certain amount of protrusion attached.

In this case, since the conductive layer 1e was formed into a sponge shape, its hardness could be lowered to about 40 ° with ASKER-C, and a further effect on vibration noise was recognized.

It is considered that this is because the hardness of the charging roller decreases and the conductive layer 1e absorbs the vibration of the charging roller due to the AC electric field.

On the other hand, in an environment of low temperature and low humidity, when the ten-point surface roughness of the conductive layer 1b was about 100 μm, spot-like charging defects were remarkably increased due to the extreme unevenness of the surface, which became a problem. It is considered that this is because charges once charged on the photosensitive drum are discharged toward the pointed portion on the surface of the charging roller, and the charge at that portion disappears. As a result, an uncharged portion having a diameter of about 0.1 μm is formed on the photosensitive drum, and the portion is not developed by regular development but is developed by reversal development. As a countermeasure, it is necessary to make the surface of the conductive layer 1b as smooth as possible. However, if the surface of the conductive layer 1b is simply smoothed, the vibrating noise becomes louder.
Resinin (manufactured by Teikoku Kagaku Co., Ltd.) amylan (CM
-8000, manufactured by Toray Industries, Inc., etc. 10-point average roughness 30 μm
It is advisable to provide the high resistance layer 1f having a thickness of 100 μm. The reason why 1f is a high resistance layer is that charges on the photoconductor drum do not discharge toward the protrusions on the 1f surface. By doing so, it became possible to reduce charging noise and reduce vibration noise. Further, by providing the high resistance layer 1f, even if a defect such as a pinhole occurs on the photoconductor drum, a large current will flow into that part, and it is possible to prevent electric charge loss in the flow direction of the photoconductor drum. You can also do things.

When the high resistance layer 1f is made of nylon resin such as resin or amylan, the resistance is about 3 digits at low temperature and low humidity.
^It also increased from ¹⁰ Ωcm to 10 ¹³ Ωm), and the problem of defective charging occurred.

Therefore, as shown in FIG. 7, the ten-point average roughness Rz of the surface
Conductive layer 1 that was smoothly processed to a thickness of 1.5 μm or less
On top of b, a high resistance layer of 1 g (80 μm thick) made of epichlorohydrin rubber, which does not increase in resistance even at low temperature and low humidity.
m), are provided. At this time, a thin surface layer 1f (with a thickness of 20 μm) of resin, amylan, etc. on top of 1 g of epichlorohydrin rubber
m) and projections 1C were provided to obtain a ten-point average roughness of 10 μm. By providing the surface layer 1f in this way, the softening agent oozes out from the epichlorohydrin rubber and adheres to the surface of the photoconductor drum, and the resistance of the extracted portion decreases and an image defect called "image deletion" occurs. Could be prevented.

In addition, as described above, the ten-point average roughness of the conductive layer 1b is 1.5 μm.
By the following, the charging failure was eliminated. 20μm for resin, amylan, etc., whose resistance increases at low temperature and low humidity.
By making the film as thin as possible and using a layer of epichlorohydrin rubber with a small resistance fluctuation of 80 μm, it has become possible to suppress the total increase in resistance. In addition, the vibration noise can be reduced by appropriately roughening the surface of the charging roller.

Further, as shown in FIG. 8, a thermoplastic elastomer (thermoplastic elastomer, manufactured by Lavalon Mitsubishi Petrochemical Co., Ltd.) 1h may be provided below the conductive layer 1b. In this case, the hardness of the charging roller can be reduced to 40 ° C. or lower with ASKER-C, and the noise countermeasure is more effective. However, since the thermoplastic elastomer 1h is insulative, the conductive layer 1h
Must have a structure capable of establishing conduction with the core metal as shown in FIG.

Further, the charging member is not limited to the roller shape but may be a blade shape as shown in FIG. 6a is a support plate for applying a voltage to the blade, and 6b is a conductive blade having a rectangular cross section with a length of 15 mm and a wall thickness of 1.5 mm.

Reference numeral 6C denotes a protruding portion which is previously provided with a recess in the mold to mold the conductive blade so that the ten-point average roughness becomes 50 μm.

The blade of this example was also able to exhibit the same effects as the charging roller.

The charging member is not limited to the charging member that uniformly charges the charged body when the latent image is formed on the photosensitive body, which is the charged body, as described above. For example, the image of the photosensitive body is transferred to the transfer material. The transfer roller can also be applied when it comes into contact with a member to be charged and an oscillating voltage is applied.

Further, the charging member includes not only a charge to the charged body but also a charge eliminating roller and a blade for removing the charge of the charged body. That is, the charging member exchanges charges with the body to be charged.

Further, although the OPC photosensitive member is used as the charged member in the above-described embodiment, the charged member is not limited to this, and various photosensitive members such as A-Si photosensitive member and Se photosensitive member and the photosensitive member are also available. Other than that, the present invention can be preferably adopted even if a dielectric drum is used.

Further, since the surface of the charging member is appropriately arranged as described above, there is an advantage that toner or talc of paper is less likely to film the photosensitive member.

EFFECTS OF THE INVENTION As described above, in the contact charging device of the present invention, the ten-point average roughness of the surface of the charging member is set to be larger than 5 μm and smaller than 100 μm. It is possible to prevent the abrasion of the member to be charged and prevent the member from being scraped, and it is possible to perform good charging.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of the contact charging device of the present invention, FIG. 2 is a perspective view of FIG. 1, and FIGS. 3 to 8 are other embodiments of the contact charging device of the present invention. FIG. 9 is a perspective view, FIG. 9 is a cross-sectional view showing another embodiment of the contact charging device of the present invention, and FIGS. 10 to 12 are explanatory views for explaining a mechanism in which a charging roller vibrates to generate sound. FIG. 13 is a sectional view when the contact charging device of the present invention is applied to an image forming apparatus. In the figure, 1 is a charging roller, 2 is a photoconductor, and 3 is a power source for applying an oscillating voltage.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Junji Araya 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Toshiharu Nakamura 3-30-2 Shimomaruko, Ota-ku, Tokyo Kya Non-Incorporated (72) Inventor Masanobu Saito 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Incorporated (56) Reference JP-A-63-149669 (JP, A) JP-A-63-208876 ( JP, 64-90466 (JP, A) JP, 2-141761 (JP, A) JP, 2-198468 (JP, A) JP, 2-222985 (JP, A)

Claims (1)

[Claims] 1. A contact charging device for charging by charging a charging member to which an oscillating voltage is applied to an object to be charged, wherein a ten-point average roughness Rz of the charging member surface is more than 5 μm and 100 μm.
A contact charging device characterized by being smaller.