JPH0269781A - Corona electrifying device - Google Patents

Abstract

PURPOSE:To prevent the deterioration of an image without causing an abnormal discharge to a photosensitive body or a shield electrode, etc., by superposing an AC voltage on a DC high voltage, generating a (+) corona current being equal to the case of only the DC high voltage efficiently by executing a stronger discharge, and using a square wave of 25% - 80% duty as the AC voltage. CONSTITUTION:When the charge give to the surface of an electrifying member is required by >=200nc/m<2> in order to electrify a member to be electrified to a desired potential, a high voltage is obtained by superposing an AC voltage on a DC high voltage. Also, a DC voltage value and on AC voltage value are set so that the polarity of a corona discharge current becomes only a component of the same polarity as that of the DC high voltage, a waveform of the AC voltage is a square wave, and a ratio of the same polarity portion as the DC voltage superposed on the square wave per one period of the square wave is 25% - 80%. In such a way, an abnormal discharge (spark discharge, etc.) to the member to be electrified, a shield electrode member, etc., is not caused, and the deterioration of an image quality can be prevented.

Description

Detailed Description of the Invention: "Industrial Application Field" The present invention relates to a corona charging device for uniformly charging a member to be charged. The present invention relates to a corona charging device that generates corona discharge by applying a superimposed voltage, and more specifically to a corona charging device that positively or negatively charges an electrostatographic imaging surface.

"Prior Art" Charging devices for uniformly charging a charged member by applying a high voltage to a corona discharge wire to generate a corona discharge are classified into the following four types based on the type of applied voltage. being classified.

■ The most common system that applies DC high voltage. Positive polarity (■) DC is applied to the corona discharge wire.
By applying a high voltage, a (1) discharge is generated, and by applying a high voltage of negative polarity (e), an O discharge is generated.

■ Systems that apply a superimposed voltage of AC voltage and DC voltage Mainly corona discharge of ■・0 polarity due to AC voltage, and the charged member is charged by the difference in the corona discharge load (current amount) of both polarities. Or one that performs θ charging. The DC voltage is an auxiliary voltage, and serves to adjust the difference in the amount of corona discharge charge between the two polarities and the zero polarity due to the AC voltage, and to keep the difference constant.

■ Systems that apply a superimposed voltage of AC voltage and DC high voltage Systems that charge the charged member to the polarity corresponding to the ■ or ○ polarity corona discharge charge determined by the DC high voltage, and the AC voltage is auxiliary. It serves to temporally vary the amount of corona current of either 2 or e polarity due to DC high voltage.

■ A system in which a special waveform voltage is applied as the applied voltage, such as distorting the AC waveform to one side or generating only pulsating current.The present applicant also published Japanese Patent Application Laid-Open No. 61-4082 regarding the improvement of the above system (■). We are disclosing the system.

The invention disclosed in the published publication ζ relates to a corona discharge device that generates corona discharge by applying a high voltage to a corona discharge wire,
The high voltage is a DC high voltage superimposed with an AC1FC voltage, and the DC voltage value and the AC voltage value are set so that the polarity of the corona discharge current is only a component with the same polarity as the DC high voltage. This is a corona discharge device with
The main objective is to obtain a stable corona discharge with substantially no unevenness in the discharge distribution along the length of one line.

``Problem to be solved by the invention'' When large-area films are formed during the manufacturing process, such as with photoreceptors generally used in electrostatic photography, abnormal growth of the film and the occurrence of pinholes are unavoidable, especially in vacuum film-forming methods. It is. If the above-mentioned abnormal growth or pinhole exists on the member to be charged, that portion becomes a minute region of low resistance, and for example, there is a phenomenon in which the portion becomes an image defect in an electrostatic image forming process.

In this way, if there is a low-resistance minute region with no charge retention ability on the charged member, the charge applied to the surface of the charged member due to corona discharge to the charged member may be reduced to 200 nc/min.
Under conditions where cm2 or more is required, even if the conventional method makes the state of the discharge wire as uniform as possible and suppresses discharge unevenness, the area around the low resistance region will be excessively charged compared to the normal charged member. A phenomenon occurred. The machine where the above phenomenon occurs (4°
4 is not clear, but it is thought to be due to the following reasons. When a low-resistance minute region exists in a member to be charged, a potential difference is generated due to a difference in charging ability between the region and a surrounding normal portion, and the electric field in the vicinity is strengthened. This intensifies the discharge of the portion of the corona charging device that faces the area, thereby increasing the charging current to the charged member and excessively charging the area around the area. Furthermore, it is necessary to apply a charge of 200 nc/cm2 or more to the surface of the charged member, that is, a larger charging current is required for the charged member, and as a result, the electric field strength on the charged member is stronger, and corona products are generated. When the influence of this phenomenon increases, abnormal growth, pinholes, etc. that occur during the film formation process become a minute low-resistance region where the above-mentioned excessive charging phenomenon occurs significantly.

In order to prevent such excessive charging phenomenon, a sufficiently strong corona discharge is performed, and a part of the total electric current resulting from this is used as a charging current for the charged member, thereby suppressing the above excessive charging phenomenon and reducing charging. In order to achieve uniformity, it is necessary to increase the total amount of discharge current, which poses a problem in that the power source used must be large with high output and high capacity. Furthermore, as the discharge current density increases, there is a problem in that abnormal discharge (spark discharge, etc.) occurs with the shield electrode member and the like. Furthermore, there is a problem in that as the total amount of discharge current increases, the amount of corona products such as ozone (05) and nitrogen oxides (NOx) increases. In addition, for the purpose of solving the above problem, that is, in order to keep the total amount of discharge current constant and strengthen the discharge, when performing discharge using a superimposed voltage of AC voltage on DC high voltage, the surface of the discharged member When it is necessary to apply a charge amount of 2oonc/cm2 or more to is 2
When a rectangular wave (of 5% or less) is used, a problem arises in that abnormal discharge (spark discharge, etc.) occurs with the charged member, the shield electrode member, etc.

"Means for Solving the Problems" The present invention relates to a corona charging device that applies a high voltage to a corona discharge wire to generate corona discharge, in which a high voltage is applied to the surface of a charging member in order to charge the member to a desired potential. When the electric charge required is at most 200 tlc or 2 liters, the high voltage is a superimposition of an alternating current voltage on a direct current high voltage, and the polarity of the corona discharge current is only a component with the same polarity as the direct current high voltage. The DC voltage value and the AC voltage value are set as follows, the waveform of the AC voltage is a rectangular wave, and the ratio of the DC voltage and the same polarity component superimposed on the rectangular wave per period of the rectangular wave is 25%.
This is a corona charging device characterized in that the electrification speed is 80 cm.

"Example" [Example 1] In FIG. 1, a drum-type photoreceptor 1 (
The charged member) is rotated in the direction of the arrow at a predetermined circumferential speed. The photoreceptor 1 is made of, for example, amorphous silicon, and there is a minute low-resistance region on the photoreceptor that does not have the ability to retain charge.

A corona discharger 2 is provided for uniformly charging the surface of the photoreceptor 1 to form an image. When forming an electrostatic photograph, the amount of charge applied to the photoreceptor 1 necessary to charge the photoreceptor 1 to a desired potential is approximately 250 nc/cm2.
It is. Other necessary process execution equipment such as an image exposure device, a developing device, a transfer device, and a photoconductor cleaning device are arranged around and around the photoconductor 1, thereby configuring the entire mechanism of an electrophotographic copying machine. However, it is omitted from the figure.

The corona discharger 2 includes a corona discharge wire 3 and a shield plate 4. A rectangular wave AC high voltage power source 5 and a DC high voltage power source 6 are connected in series between the corona discharge wire 3 and the ground. DC high voltage VD is applied to the corona discharge wire 3 by these two power supplies 5 and 6 in series.
Voltage VDC+VP where square wave AC voltage VPP is superimposed on C
P is applied. The shield plate 4 is grounded.

In this example, the output vpp of the square wave AC high voltage power supply 5 has a frequency of 5 oaHz and a voltage of 8.5 KVpp (peak
lo peak), and the output voltage vDc of the DC high voltage power supply 6 is approximately 4.35 KV. Further, the positive voltage output (duty) per rectangular wave period is 50% of the total.

Under this voltage condition, the corona discharge power source I2 flows from the corona discharger 2 to the photoreceptor 1, and the surface of the photoreceptor is charged. As mentioned above, the amount of charge charged to the photoreceptor 1 by the charging current to bring the surface of the photoreceptor 1 to the desired charging potential is 250 nc2, and the DC high voltage VOC and the rectangle superimposed thereon are This value is obtained by the wave AC voltage vpp.

The table below shows the results for each case in which a rectangular wave AC voltage VPP with various proportions of positive voltage output per cycle is superimposed on the DC high voltage ■Dc while keeping the corona discharge current I2 constant. , shows the results of measuring the image density difference and the degree of unevenness on the image with respect to a uniformly charged area around the low resistance area existing on the photoreceptor 1 when an image is actually output.

X: Below practical level Δ: Almost practical level ○: Above practical level As is clear from the table, by superimposing square wave AC voltage VPP on DC high voltage VDC and making the peak voltage vP about 7.4 KV or more, the image can be improved. There will be almost no unevenness on the top. In order to prevent spark discharge, it is necessary to avoid increasing the peak voltage vP more than necessary, and in this example, the duty of the rectangular wave AC voltage VPP is 50% and the peak voltage is 8.5 KV.

[Example 2] Figure 2 shows another example, and this example shows a total corona current amount of 1
D on the shield plate 4 of the corona discharger 2 for the purpose of reducing
A bias voltage VB of the same polarity as the C high voltage power supply 6 is applied from a bias power supply 7, and the other configuration is the same as that of the embodiment shown in FIG. Bias voltage VB may be applied by a linear or nonlinear element.

The voltage applied to corona discharge a3 is V. C (4,35K
V) +Vpp (8,7KV, approximately 5ooHz square wave)
When L and bias voltage VB are set to 1Kv, the total current amount is 1
1 reduces the corona discharge current I2 to 639 μA.
The amount of charge applied to the photoreceptor 1 by 25 is the same as in the above example.
At 0 nc/an2, a photoreceptor potential equivalent to that of the above example can be obtained. Further, the ratio of positive voltage output per cycle of the rectangular wave AC voltage vPi'' was set to 25q6.

The table below shows the results for each case in which a rectangular wave AC voltage "PP" in which the proportion of positive voltage output per cycle is varied is superimposed on the above DC high voltage VDC while keeping the corona discharge current 2 constant. Photoconductor 1 when actually outputting an image
This figure shows the results of measuring the difference in image density and the degree of unevenness on the image with respect to the uniformly charged area around the low-resistance area that exists above.

×: Below practical level Δ: Above practical level O: Above practical level As is clear from the table, DC high voltage Vnc i square wave A
C voltage VPP is superimposed, and the peak voltage vP is approximately 7.1Kv.
By doing the above, unevenness will not appear on the image.

[Embodiment 3] In this embodiment, as shown in FIG. 3, a grid electrode 8 is provided in the corona discharger 2 for the purpose of controlling the potential on the surface of the photoreceptor. voltage vG
is used by applying it from a bias power supply 7, and the other configuration is the same as that of the first embodiment shown in FIG. The bias voltage vG may be applied by a linear or nonlinear element. The shield plate 4 is grounded.

The voltage applied to the corona discharge wire 3 is VDC (4.4KV
) +V, (8,8KV, approx. 50oHz square wave)
The above-mentioned surface potential can be obtained by setting the bias voltage vG to a voltage substantially equal to the desired surface potential of the photoreceptor 1 (approximately 450 V in this example). Also, square wave A
The duty of the positive voltage output of the C voltage vpp was set to 50 inches.

The table below shows the square wave AC with varying duty to the above DC high voltage VDC while keeping the corona discharge current constant.
Results of measuring the image density difference and degree of unevenness on the image with respect to the uniformly charged area around the low resistance area existing on the photoreceptor when an image is actually output in each case where the voltage vpp is superimposed. This shows that.

×: Practical level or higher Δ: Practical level ○: Practical level or higher The unevenness almost disappears. Further, it is necessary to avoid increasing the peak voltage more than necessary in order to prevent spark discharge, and in this example, the duty of the rectangular wave AC voltage VPP is 50% and the peak voltage is 8.8 KV.

By the way, the effect of suppressing excessive charging around the minute low resistance region existing on the photoreceptor due to the superimposed voltage of the DC high voltage and the AC voltage is thought to be due to the following phenomenon. That is, by using the above-mentioned superimposed voltage, the photoreceptor direction current is effectively equivalent to a DC high voltage, but a stronger discharge is instantaneously performed. In other words, the total number per unit time is 1! The charging current for the photoreceptor is larger, and this is used to charge the photoreceptor. When the discharge is strengthened and the total current is increased, the influence of the electric field in the vicinity of the minute low resistance region on the photoreceptor on the discharge in the opposing portion becomes relatively small. It is thought that this suppresses excessive charging around the area and enables more uniform charging.

Although the present invention has been particularly described based on (1) discharge, it is not limited thereto. Further, the bias voltage VB applied to the shield plate 4 is not limited to direct current or alternating current.

〔Effect of the invention〕

As explained above, for example, when charging a photoreceptor with a small low resistance region to a desired potential during corona discharge, superimposing an AC voltage on a high DC voltage is preferable to performing a corona discharge with only a high DC voltage. , by generating a corona current that is effectively equivalent to the case of only DC high voltage, the duty is 25% as an AC voltage.
By using a ~80% rectangular wave, when the amount of charge applied to the photoconductor needs to be 200 nc/an' or more, abnormal discharge does not occur with the photoconductor or the shield electrode, and therefore uneven charging due to this can be avoided. While maintaining stable discharge without image deterioration, suppressing the phenomenon in which the periphery of the low resistance area is excessively charged, the image density becomes higher than other uniformly charged areas, and the image quality deteriorates, In practice, the effect of preventing the appearance of unevenness due to density differences on a copied image was obtained.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of the corona discharge device of Example 1, Fig. 2 is a schematic diagram of the corona discharge device of Example 2, and Fig. 3 is a schematic diagram of the corona discharge device of Example 3.
FIG. 2 is a schematic diagram of a corona discharge device. 1. Photoconductor 2. Corona discharge device 3. Corona discharge a 4. Shield plate 5. Square wave AC high voltage power supply
6. DC high voltage power supply 7. Bias power supply 8. Grid electrode. Figure 1

Claims (1)

[Claims] 1. In a corona charging device that generates corona discharge by applying a high voltage to a corona discharge wire, in order to charge the charged member to a desired potential, it is necessary to apply a charge of 200 nc/cm^2 or more to the surface of the charging member. In this case, the high voltage is a DC high voltage superimposed with an AC voltage, and
The DC voltage value and the AC voltage value are set so that the polarity of the corona discharge current is only a component with the same polarity as the DC high voltage, and the waveform of the AC voltage is a rectangular wave, and the waveform of the AC voltage is a rectangular wave per cycle of the rectangular wave. The ratio of the same polarity as the superimposed DC voltage is 25% ~
A corona charging device characterized in that the charging rate is 80%.