JPH03100674A - Electrifier - Google Patents

Abstract

PURPOSE:To reduce the occurrence of oscillation sound without losing uniformity of electrification by setting the inter-peak voltage of an oscillating electric field at >=two times the absolute value of the electrification start voltage of a body to be charged and specifying relation among the frequency of the oscillating electric field, the travel speed of the body to be charged, the contact width of the body to be charged and a contact member in the travel direction of the body to be charged, and a threshold frequency. CONSTITUTION:A high voltage power source 3 as an electric field forming means to form the oscillating electric field between a charging roller 2 as the contact member and a photosensitive drum 1 that is the body to be charged impresses a voltage to the conductive core bar 2a of the charging roller 2. At such a case, the inter-peak voltage of the oscillating electric field is set at >= two times the absolute value of the electrification start voltage of the body 1 to be charged, and also, the relation expressed in equation I can be satisfied assuming the frequency of the oscillating electric field as f[Hz], the travel speed of the body to be charged as vp[mm/sec], the contact width of the body 1 to be charged with the contact member 2 in the travel direction of the body to be charged as l[mm], and the threshold frequency as f1[Hz]. In such a way, the electrification is performed uniformly, and the occurrence of the oscillation sound is reduced.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a charging device that charges an object to be charged by forming an electric field between an object to be charged and a contact member that contacts the object to be charged. be.

[Background technology]

For example, in image forming devices such as electrophotographic devices (copiers, optical printers, etc.) and electrostatic recording devices, devices that charge the surface of an image carrier as a charged body such as a photoreceptor or dielectric are Corona discharge devices have been widely used in the past.

A corona discharge device is effective as a means for uniformly charging the surface of an object to be charged, such as an image carrier, to a predetermined potential. but,
It requires a high-voltage power supply and has problems such as the generation of undesirable ozone due to corona discharge.

In contrast to such corona discharge devices, the contact charging device, which charges the surface of the charged object by bringing the charging member to which a voltage is applied as described above into contact with the surface of the charged object, can reduce the voltage of the power supply and generate ozone. Because of its advantages such as small amount of charge, it is attracting attention as a charging treatment device for the surface of photoreceptors, dielectrics, etc., and other charged objects instead of corona discharge devices in image forming apparatuses, for example. Research on its practical application is underway.

[Problems to be Solved by the Invention] However, when a contact charging device is used, there is a problem in that spot-like charging unevenness occurs on the charged object compared to when a corona charging device is used.

In order to prevent this charging unevenness, it has been found that superimposing an alternating current voltage on the direct current voltage applied to the charging member can be effective to some extent.

As a result of experiments conducted by the present applicant, when the frequency of this alternating current voltage falls below a certain value, periodic charging unevenness occurs due to this. This charging unevenness is caused by the frequency f of the AC voltage and the moving speed (process speed) v of the image carrier as the charged object.
Depends on pq and the contact width l between the charged object and the charging member, p ->f (Hz)! Occurs in the case of

Furthermore, when the frequency becomes too high, vibrations occur between the charging member that contacts the charged object and the charged object, resulting in the generation of a harsh vibration sound.

[Purpose of the invention]

The present invention has been made in view of the above points, and an object of the present invention is to provide a charging device that performs charging uniformly and reduces the generation of ozone and vibration noise.

[Structure of the invention]

In order to achieve the above object, the present invention includes a contact member that contacts a movable object to be charged, and an electric field forming means that forms an oscillating electric field between the contact member and the object to be charged. , in a charging device that charges an object to be charged, the peak-to-peak voltage of the oscillating electric field is set to be at least twice the absolute value of the charging start voltage of the object to be charged, and the frequency of the oscillating electric field is f (
Hz), and the moving speed of the charged object is v p (mm/s
e c ), the contact width between the charged body and the contact member in the moving direction of the charged body is l [mm), and the limit frequency is f
1 [Hz].

〔Example〕

FIG. 1 is a sectional view showing an embodiment of the charging device of the present invention.

1 is a photoreceptor drum with a conductive pipe made of Al2 or the like as a base and an organic photoreceptor coated on the surface layer.Although the organic photoreceptor is used here, amorphous silicon, amorphous silicon, etc.
A general photoreceptor such as Se may be used. Further, the photoreceptor may have a belt shape instead of a photoreceptor drum shape.

Reference numeral 2 denotes a charging roller which is a charging member, and here, it is constructed by covering a conductive core metal 2a with conductive rubber 2b. 106Ω・cm on the surface layer to prevent
It is preferable that a dielectric layer having a high resistance of ~1012 Ω·c, m is coated.

The charging roller 2 as a contact member is in contact with the photoreceptor drum l, which is the object to be charged, with a nip width (contact width) of about 1 mm in the moving direction of the photoreceptor drum 1, and is driven by the rotation of the photoreceptor drum l. and rotate.

A high voltage power source 3 serves as an electric field forming means for forming an oscillating electric field between the charging roller 2 and the photosensitive drum l, and applies a voltage to the conductive core metal 2a of the charging roller 2. This voltage is an AC voltage with a peak-to-peak voltage of 1500V and -700V.
This is the superimposed voltage with the DC voltage.

This oscillating electric field is an electric field that changes periodically over time.

Through experiments conducted by the present applicant, it has been found that if the peak-to-peak voltage of the AC voltage at this time is 1100 V or more, the photoreceptor drum 1 is uniformly charged. Here the voltage between peaks is 1100V
refers to the photosensitive drum (organic photoconductor) that is the charged object.
This corresponds to twice the absolute value of the charging start voltage of -550V.

That is, when the peak-to-peak voltage of the oscillating electric field formed between the photosensitive drum 1 and the charging roller 2 is set to be at least twice the charging start voltage of the photosensitive drum 1, uniform charging is performed. Here, the charging start voltage of the charged object is the DC voltage at which the charged object is initially charged when only DC voltage is applied to the contact charging member and the voltage value is gradually increased. It is a value. The experimental results are shown in FIGS. 4 and 5.

Figure 4 is a graph showing the relationship between the peak-to-peak voltage VPP applied to the charging roller and the surface potential of the OPC photoreceptor, and Figure 5 is a graph showing the relationship between the DC voltage vDc applied to the charging roller and the surface potential of the OPC photoreceptor. This is a graph showing.

The spotty charging unevenness could be solved by applying the above-mentioned peak-to-peak voltage to the charging member, but as the frequency f of the AC voltage used to form the oscillating electric field was reduced, the frequency Correspondingly, periodic unevenness may occur in the moving direction of the photoreceptor drum l.

Therefore, we investigated by changing the frequency f (Hz), the moving speed of the photosensitive drum (process speed) v p (mm/5ec), and the contact width f (mm) between the photosensitive drum 1 and the charging roller 2 in the direction of drum movement. I did it.

Using a charging roller with a diameter of 12 mm and a core metal diameter of 6 mm, Vp = 50 mm/sec, f = 50H
When z, 1 = 1 mm, charging unevenness occurs at a pitch of 1 mm, but when f = loOHz, the pitch becomes 0.5 mm. The unevenness becomes less noticeable (it becomes more noticeable. If you further increase the frequency to 200Hz, the unevenness disappears at all.

On the other hand, when a charging blade in contact with a counter is used instead of the charging roller as shown in Fig. 2, as shown in the table, even when Vp is 50 mm/see and f = 50 Hz,
The unevenness was not that noticeable, and when I set it to 100Hz, it became almost invisible.

As there is a slight difference between the blade and the roller, the cause of the difference is the charging width I! (See Figure 3. Discharge occurs in this region.) Considering this, we changed the charging width l by changing the angle between the blade and the photoreceptor, and found the following.

That is, if the oscillating electric field generated by the applied voltage is not applied one or more times while the photoreceptor passes through the charging width l, uneven charging pitch will occur, and in order to prevent unevenness, P - < f! ...The condition (1) is necessary. Naturally, this means that in the case of rollers, it is possible to increase the diameter, and in the case of blades, it is possible to reduce the contact angle (by doing so, l becomes thicker), and therefore the minimum frequency can be reduced. It will become,
A similar effect can also be obtained by slowing down the process speed.

In this way, suppressing the frequency to a certain level means that the frequency f
(This is because the larger the width, the louder the vibration noise will be.)

Therefore, Table 1 shows the results of evaluating the uniformity of charging and the vibration noise by varying the frequency f1 and the process speed Vp with l=1 mm. Regarding charging uniformity, the formula (
The conditions of 1) and the experimental results almost matched.

As for vibration noise, if you reduce it below 1000Hz, it becomes almost unnoticeable, and furthermore, if you reduce it below 800Hz, there is almost no problem.Therefore, the limit frequency f is 1000Hz.
.

Preferably it is 800Hz.

Furthermore, when f was made smaller than 500 Hz, no vibration sound was heard at all.

Table 1 In the above embodiment, as the waveform of the AC voltage, not only a sine wave but also a triangular wave, a rectangular wave, etc. can be used.

Although not shown, this charging device can be applied to an image forming apparatus, and after charging a photoreceptor with the charging device, the photoreceptor is exposed to light according to image information by an exposure means to form a latent image, After this latent image is developed with toner by a developing device, it is transferred onto a transfer material by a transfer device to form an image.

〔Effect of the invention〕

As explained above, according to the present invention, the peak-to-peak voltage of the oscillating electric field is made to be at least twice the absolute value of the charging start voltage of the charged object, and the frequency of the oscillating electric field is set to f (Hz), The moving speed of the body is Vp [mm/sec], and the contact width between the charged body and the contact member in the moving direction of the charged body is f [mm].
, when the limit frequency f1 [Hz] is set, Vp −<f<f'H (f1 is 1000 Hz), so generation of vibration noise can be reduced without losing charging uniformity.

[Brief explanation of drawings]

1 and 2 are cross-sectional views showing embodiments of the charging device of the present invention, FIG. 3 is a cross-sectional view illustrating the charging width l of the charging device, and FIG. 4 is the peak-to-peak voltage applied to the charging member. FIG. 5 is a graph showing the relationship between the DC voltage applied to the charging member and the surface potential of the photoreceptor. In the figure, 1 is a photoreceptor, 2 is a charging member, and 3 is a power source.

Claims (1)

[Scope of Claims] A contact member that contacts a movable object to be charged, and an electric field forming means that forms an oscillating electric field between the contact member and the object to be charged, and charges the object to be charged. In the charging device, the peak-to-peak voltage of the oscillating electric field is set to be at least twice the absolute value of the charging start voltage of the object to be charged, the frequency of the oscillating electric field is f [Hz], and the moving speed of the object to be charged is V_P [ mm/
sec], V_P/l<f<f_1 [Hz] (where f_1 =10
00).