JPH063929A - Contact electrostatic charging method - Google Patents

Abstract

(57) [Summary] (Correction) [Purpose] A contact charging method in which a charging member 10 to which a voltage is applied is brought into contact with the member to be charged 1 to charge the member to be charged 1 To reduce the "charging noise" without any adverse effect, and to enable uniform charging with halftone and no pitch unevenness even in high-speed image forming apparatuses. [Structure] The applied voltage is a voltage obtained by superimposing an AC voltage that is not a sinusoidal change on a DC voltage, and the AC voltage has a peak value in a plus direction and a minus direction within one period (T), and each has a peak value. Assuming that the time in which the component in the direction is not 0 is t _{+ in} the positive direction and t _{− in} the negative direction, the relationship of 0 <t ₊ ≦ T / 10 0 <t ₋ ≦ T / 10 is satisfied in one cycle (T). A contact charging method characterized by satisfying.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a contact charging method in which a charging member to which a voltage is applied is brought into contact with a member to be charged to charge the surface of the member to be charged (including static elimination).

[0002]

2. Description of the Related Art Conventionally, as a means for charging the surface of an image bearing member such as a photoconductor or a dielectric as a member to be charged in an image forming apparatus such as a copying machine or a recording device such as an electrophotographic system or an electrostatic recording system. A corona discharger, which is a non-contact type charging device such as a corotron or a scorotron having a good uniform charging property, is widely used.

However, the corona discharger requires an expensive high-voltage power source, requires a space such as itself and a shield space for the high-voltage power source, and often produces corona products such as ozone. Requires additional means / mechanism,
There is a problem in that they are factors that increase the size and cost of the device.

Therefore, recently, the use of a contact charging type device is being considered in place of the corona discharger which has the above-mentioned problems.
In the contact charging, the surface of the image carrier serving as a member to be charged is brought into contact with a charging member (conductive member) to which a voltage is applied to charge the surface of the image carrier to a predetermined potential. -91253), blade charging type
Nos. 56-194349 and 60-147756), charging / cleaning combined type (JP-A-56-165166) and the like have been devised.

The voltage applied to the charging member is generally 1-2.
What uses only a DC (direct current) voltage of KV, and Japanese Patent Laid-Open No. 63-
As disclosed in Japanese Patent Publication No. 149669, etc., an oscillating voltage (alternate voltage; a voltage whose voltage value periodically changes with time), for example, A
There is one that uses a superimposed voltage of a C (AC) voltage and a DC voltage. The waveform of the oscillating voltage or AC voltage component is a sine wave (s
(in wave), rectangular wave, sawtooth wave, triangular wave, pulse wave, or a rectangular wave voltage formed by periodically turning on / off a DC power supply.

The above-mentioned contact charging (DC applying method) of applying only the DC voltage has an advantage that an inexpensive one having a low applied voltage and a simple power source can be used, but on the other hand, spot-like charging unevenness is likely to occur. In addition, the latitude is small for obtaining uniform charging because the charging member is not susceptible to dirt and the like.

On the other hand, the latter contact charging (AC application method) in which an oscillating voltage is applied can significantly improve spot-like charging unevenness, and the power source is slightly smaller than that in the contact charging in which only DC voltage is applied. Although it is complicated and costly, it has a large latitude for obtaining a uniform charging property. The oscillating voltage is
An oscillating voltage in which an AC voltage having a peak-to-peak voltage that is twice or more the charging start voltage of the body to be charged is superimposed on the DC voltage is effective.

[0008]

However, in the case of contact charging of the AC application system in which an oscillating voltage is applied, the oscillating voltage applied causes an oscillating movement of the charging member, and the charged body to which the charging member is pressed is also contacted. It has a drawback that it vibrates and produces a so-called "charging noise".

This charging sound has a frequency of, for example, twice the frequency of the AC voltage component of the vibration voltage applied to the charging member, and if the frequency is low (for example, 200 Hz or less), it gives offensive and unpleasant impression. However, as the frequency increases, it gradually becomes annoying and unpleasant.

Therefore, in order to prevent the charging sound from being offensive to the ears, it is desirable to set it to 200 Hz or less.

However, if the frequency is set too low, in the image forming apparatus, in the halftone image, [process speed (mm / sec) / frequency (H
z)] mm 2 pitch irregularity occurs. This pitch unevenness is 0.1 mm
It is 0.15m though it is not visible even with the naked eye
If the pitch is m or more, the image is not recognized because it is visually recognized.

Considering the above points, the process speed at which the pitch unevenness is not recognized and the charging noise is not felt at the frequency of 200 Hz or less must be at least 30 mm / sec or less.

However, in reality, most electrophotographic apparatuses have a process speed of 30 mm / sec or more, and in an image forming apparatus having this process speed, when the above-mentioned AC charging type contact charging is used, there is some problem. It is necessary to reduce the charging noise by means or to eliminate the noise.

The charging sound changes depending on the shape and material of the charging member. If the charging member has a blade shape (charging blade) and is fixed to the member to be charged, it rotates in a roller shape with respect to the member to be charged. The charging noise tends to be louder than that of a charging member (charging roller) that is being charged.

As described above, the oscillating voltage waveform applied to the charging member is generally a sin wave, a rectangular wave, a sawtooth wave, a triangular wave, or the like, but "charge noise" is generated in any waveform. Will end up. Experimentally, the sin wave seems to have the smallest "charged sound", and the waveform that has been put to practical use is also the sin wave (waveform (d) in FIG. 2).

As a method of reducing the "charging sound", there are a method of suppressing vibrations of the body to be charged and a method of preventing sound from leaking outside the image forming apparatus.

As a method of suppressing the vibration of the charged body,
Taking an object to be charged, for example, an electrophotographic photosensitive drum as an example, it is conceivable to fill the drum and increase the weight of the drum.

However, this is contrary to the current direction of size and weight reduction of the apparatus, and particularly in the image forming apparatus in which the member to be charged is integrated into the process cartridge, the weight of the cartridge is increased and the cost is increased. There is.

Also, as for sound insulation, there is a problem that the size of the apparatus is increased by adding a sound insulation member.

Therefore, according to the present invention, it is possible to reduce the "charging noise" without the adverse effects of increasing the size and weight of the device.
It is another object of the present invention to provide a contact charging method capable of performing uniform charging in halftone with no pitch unevenness even in a fast image forming apparatus.

[0021]

The present invention is a contact charging method characterized by the following.

(1) In the contact charging method in which a charging member to which a voltage is applied is brought into contact with a member to be charged to charge the member to be charged, the applied voltage is superimposed on the DC voltage with an AC voltage that does not change sinusoidally. The AC voltage has a peak value in the plus direction and the minus direction within one cycle (T), and the time when the component in each direction is not 0 is t _{+ in} the plus direction and t _{− in} the minus direction. Then, the contact charging method is characterized in that the relationship of 0 <t ₊ ≦ T / 10 0 <t ₋ ≦ T / 10 is satisfied within one cycle (T). (2) The contact charging method according to (1), wherein the peak-to-peak voltage in one cycle of the AC voltage is not less than twice the charging start voltage of the body to be charged.

[0023]

When the AC voltage component of the oscillating voltage applied to the charging member has a waveform satisfying the above relationship, there is no adverse effect of increasing the size and weight of the device, as shown in the experimental results of the examples described later, Can be reduced.

It was also confirmed that even in an image forming apparatus having a high speed, uniform charging with halftone and no pitch unevenness is possible.

The reason why the AC voltage component waveform satisfying the above relation is effective in reducing the noise level (charging sound level) is that the vibration energy in the charging member is reduced by reducing the vibration component in one cycle. it is conceivable that.

[0026]

【Example】

<Embodiment 1> FIG. 1 is a schematic configuration diagram of a main part of an example of an image forming apparatus adopting the contact charging method of the present invention.

Reference numeral 1 denotes a rotary photosensitive drum (electrophotographic photosensitive member as an image bearing member (charged member); in this example, an OPC photosensitive layer 1a having a thickness of 25 μm and a dielectric constant of about 3 is formed on a conductive drum substrate 1b made of A1. It is formed) and is rotationally driven in the clockwise direction A indicated by an arrow at a predetermined process speed.

In the present embodiment, the image carrier 1 is a drum type, but it may be a rotating belt type or the like. In either case, it is of course possible to use seamless ones, and those with seams can also be used if each copying step is performed by obtaining a synchronizing signal.

Reference numeral 2 is a short focus lens array as an exposure means for forming a latent image on the photosensitive drum 1, 3 is a developing device, 4 is a transfer roller as a transfer means, and 6 is a sheet feeding unit (not shown). A timing roller (registration roller) that synchronizes the transfer material P conveyed sheet by sheet with the rotation of the photosensitive drum 1 and feeds the transfer material P between the photosensitive drum 1 and the transfer roller 4 (transfer portion), and 7 is a timing roller 6. The transfer guide serves as a guide for the transfer material P arranged between the transfer roller 4 and the transfer roller 4.

Reference numeral 8 denotes a conveying portion for introducing the transfer material P, which has undergone the image transfer between the photosensitive drum 1 and the transfer roller 4, into a fixing device (not shown), and 9 denotes a remaining portion on the photosensitive drum 1 after the image transfer. A cleaning device for removing toner and the like, 9a is a cleaning blade, and 10 is a charging roller as a contact charging member that contacts the photosensitive drum 1 after cleaning to uniformly charge the photosensitive drum 1.

The charging roller 10 is made by adhering a conductive rubber layer 10a to a metal cored bar 10b, and a voltage is applied from a power source E to the cored bar 10b.

In the image forming apparatus of this example, a process cartridge 20 in which four process devices including a photosensitive drum 1, a developing device 3, a cleaning device 9 and a charging roller 10 are collectively assembled in a predetermined positional relationship with each other.
The cartridge 20 can be inserted into the main body of the image forming apparatus along a supporting rail (not shown) in a direction perpendicular to the drawing, and can be detached from the main body of the apparatus. is there. By sufficiently inserting and mounting the process cartridge 20 in the apparatus main body, the apparatus main body side and the process cartridge 20 side are mechanically and electrically coupled to each other, and the image forming apparatus becomes operable. Since the principle and process of image formation belong to the public knowledge, description thereof will be omitted.

(Experiment) In the image forming apparatus shown in FIG. 1, the noise level of the apparatus main body was measured by changing the waveform of the AC voltage component of the vibration voltage applied to the charging roller 10.

In the experiment, the AC voltage component is shown in FIG.
Four waveforms A _{1 to} A ₄ shown in (b), (c), and (d)
Was generated by an arbitrary waveform generator AG1200 manufactured by Yokogawa Electric Co., Ltd., and a DC voltage was superimposed on the AC voltage amplified by an amplifier (200 times) to apply the DC voltage to the core metal 10b of the charging roller 10. did.

For the four waveforms A _{1 to} A _{4 in} FIG. 2, the peak-to-peak voltage is constant. In the waveform chart, the horizontal axis represents time t and the vertical axis represents amplitude y.

.. Waveform A _{1 The} waveform A ₁ has the following amplitude y during one period T.

I) 0 ≦ t <T / 20 y = 10 * sin (20πt / T) ii) T / 20 ≦ t <T / 2 y = 0 iii) T / 2 ≦ t <11 T / 20 y = 10 * Sin (20πt / T + π) iv) 11T / 20 ≦ t <T y = 0. Waveform A ₂ Waveform A ₂ has the following amplitude y during one period T.

I) 0 ≦ t <T / 10 y = 10 * sin (10πt / T) ii) T / 10 ≦ t <T / 2 y = 0 iii) T / 2 ≦ t <3 T / 5 y = 10 * Sin (10πt / T + π) iv) 3T / 5 ≦ t <T y = 0. Waveform A ₃ Waveform A ₃ has the following amplitude y during one period T.

I) 0 ≦ t <T / 5 y = 10 * sin (5πt / T) ii) T / 5 ≦ t <T / 2 y = 0 iii) T / 2 ≦ t <7 T / 10 y = 10 * Sin (5πt / T + π) iv) 7T / 10 ≦ t <T y = 0. Waveform A ₄ Waveform A ₄ is a conventionally used sine wave.

.. Applied bias condition for charging roller Frequency 400 Hz Peak voltage 2 KV DC voltage -600 V. Charging roller condition Outer diameter Φ12 Core metal diameter Φ6 Roller resistance 5 × 10 ⁶ Ω Roller hardness 60 ° Pressing force 1 kgf. ． Charging sound measurement conditions Measurement position 1m from the front of the device main unit Paper non-passing, drum rotation (process speed 50mm / sec) Measuring instrument Rion sound level meter (NL-02) A characteristic La eq. (Integrated value for 1 minute) Background noise 40 dB. Results; Table 1 shows the measurement results.

[0041]

[Table 1] As is clear from Table 1, the noise level of the waveform A ₁ is lower than that of the sin wave (waveform A ₄ ) of the conventional example.

Further, the waveform A ₃ has a higher noise level than the waveform A ₄ .

As can be seen from Table 1, the noise level decreases in the order of waveform A ₃ , waveform A ₂ and waveform A ₁ ,
The level of the conventional example (waveform A ₄ ) is slightly higher than that of the waveform A ₂ . The difference between the waveforms A ₁ , A ₂ , and A _{3 is} the difference in the time when the component of the oscillating electric field in the plus direction or the minus direction is (non-zero), and in the waveform A ₁ , the time is 1 / th of the period T, respectively. 20, the time is 1/10 in the waveform A ₂ , and the time is 1 in the waveform A ₃ .
/ 5.

Therefore, it can be seen that the noise level becomes smaller as the time in which there is a plus or minus component of the oscillating electric field is shorter and the time without the oscillating component is longer in one period.

In particular, it has been found that the noise level can be suppressed to a level smaller than that of the conventional sin waveform if the plus-direction component or the minus-direction component is shorter than 1/10 of the cycle.

Further, when image evaluation was carried out with the waveforms A ₁ , A ₂ and A ₃ , a halftone image equivalent to a conventional triangular wave or sin wave was obtained, and a good image without uneven charging was obtained.
The halftone pitch has a process speed of 50 m.
Since it is m / sec, for a frequency of 400 Hz,
The image quality was 0.125 mm, and the image quality was sufficient without being noticeable to the naked eye.

The reason why the above waveform is effective in reducing the noise level is considered to be that the vibration energy of the charging member is reduced by reducing the vibration component within one cycle.

Example 2 The AC voltage component of the vibration voltage applied to the charging roller 10 is shown in FIGS.
(C) ・ (d) Four waveforms B ₁・ B ₂・ B ₃・ B ₄
I chose

.. Waveform B ₁ Waveform B ₁ has the following amplitude y during one period T.

I) 0 ≦ t <T / 80 y = 800 / T * t ii) T / 80 ≦ t <T / 40 y = −800 / T * t + 20 iii) T / 40 ≦ t <T / 2 y = 0 iv) T / 2 ≦ t <41T / 80 y = −800 / T * t + 400 v) 41T / 80 ≦ t <21T / 40 y = 800 / T * t−420 vi) 21T / 40 ≦ t <T y = 0. Waveform B ₂ Waveform B ₂ has the following amplitude y during one period T.

I) 0 ≦ t <T / 40 y = 400 / T * t ii) T / 40 ≦ t <T / 20 y = −400 / T * t + 20 iii) T / 20 ≦ t <T / 2 y = 0 iv) T / 2 ≦ t <21T / 40 y = −400 / T * t + 200 v) 21T / 40 ≦ t <11T / 20 y = 400 / T * t−220 vi) 11T / 20 ≦ t <T y = 0. Waveform B ₃ Waveform B ₃ has the following amplitude y during one period T.

I) 0 ≦ t <T / 20 y = 200 / T * t ii) T / 20 ≦ t <T / 10 y = −200 / T * t + 20 iii) T / 10 ≦ t <T / 2 y = 0 iv) T / 2 ≦ t <11T / 20 y = −200 / T * t + 100 v) 11T / 40 ≦ t <3T / 5 y = 200 / T * t−120 vi) 3T / 5 ≦ t <T y = 0. Waveform B ₄ Waveform B ₄ is a conventional example called a so-called triangular wave. The waveform B ₄ has the following amplitude y during one period T.

I) 0≤t <T / 4 y = 40 / T * t ii) T / 4≤t <3T / 4 y = -40 / T * t + 20 iii) 3T / 4≤t <T y = 40 / T * t-40. The applied bias condition for the charging roller 10, the charging roller condition, and the charging sound measurement condition are the same as those in the first embodiment.

.. Results: Table 2 shows the measurement results.

[0055]

[Table 2] As is clear from Table 2, the noise levels of the waveforms B ₁ , B ₂ , and B ₃ are lower than that of the waveform B ₄ (triangular wave) of the conventional example.

[0056] Also when compared in a waveform _{B 1, B 2, B 3} , waveform B _1, waveform B _2, in the order of the waveform B ₃ low noise level.

The difference between the waveforms B ₁ , B ₂ and B _{3 is} the difference in the time when there is a positive or negative component of the oscillating electric field (not 0). In the waveform B ₁ , respectively,
That time is 1/40 of the period T, 1/20 of the period T in the waveform B ₂ , and T 1 in the waveform B ₃ .
1/10 of that.

Therefore, the noise level becomes shorter as the time in which there is a plus or minus component of the oscillating electric field during one cycle (the time occupied by the oscillating component in one cycle) is shorter and the time without the oscillating component is longer. I understand.

In particular, if the component in the plus direction or the component in the minus direction is shorter than 1/10 of one cycle, the noise level of the conventional triangular wave can be suppressed.

Further, when image evaluation was performed with each waveform of B ₁ , B ₂ , and B _3, a halftone image equivalent to a conventional triangular wave or sin wave was obtained, and a good image without charge unevenness was obtained. Also, the process speed of the halftone pitch is 5
Since it was 0 mm / sec, it was 0.125 mm with respect to the frequency of 400 Hz, and the image quality was sufficient without being noticeable to the naked eye.

The reason why the above waveform is effective in reducing the noise level is as in the case of the first embodiment.
It is considered that the vibration energy of the charging member is reduced by reducing the vibration component within one cycle.

[0062]

As described above, in the contact charging method, the bias applied to the charging member is a DC voltage superimposed with an AC voltage that is not a sinusoidal change, and the AC voltage is within one cycle (T). positive direction and has a peak value of the negative direction, and the positive direction t ₊ time component in each direction is not zero, the negative direction t in _- when the 0 in one cycle (T) <t ₊ By applying a bias satisfying the relationship of ≤T / 10 0 <t _- ≤T / 10, "charge noise" can be obtained without adverse effects such as size increase, weight increase and cost increase of the device.
It was possible to reduce the level of, and it was possible to secure a good charging property without unevenness equivalent to that of the conventional waveform.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an example of an image forming apparatus that employs a contact charging method according to the present invention.

2 (a), (b), (c), and (d) are various waveforms A ₁ A ₂ A ₃ A ₄ of the AC voltage component of the oscillating voltage applied to the charging roller in Example 1, respectively. 1 cycle diagram

3 (a), (b), (c), and (d) are various waveforms B ₁ , B ₂ , B ₃ , B ₄ of the AC voltage component of the vibration voltage applied to the charging roller in Example 2, respectively. 1 cycle diagram

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image-bearing member (electrophotographic photosensitive member) as a member to be charged 10 Contact charging member (charging roller) E Charging bias applying power source 2 Short focus lens array 3 Developing device 4 Transfer roller 9 Cleaning device

Claims (2)

[Claims] 1. A contact charging method in which a charging member to which a voltage is applied is brought into contact with a body to be charged to charge the body to be charged, wherein an AC voltage which is not a sinusoidal change is superimposed on the DC voltage. The AC voltage has a peak value in which the plus direction is the minus direction within one cycle (T), and the time when the component in each direction is not 0 is the plus direction.
A contact charging method characterized by satisfying a relationship of 0 <t ₊ ≦ T / 10 0 <t ₋ ≦ T / 10 in one cycle (T), where _{+ is} the negative direction and t ₋ is the negative direction. 2. The contact charging method according to claim 1, wherein the peak-to-peak voltage in one cycle of the AC voltage is not less than twice the charging start voltage of the member to be charged.