JPH01309076A - Conductive brush electrifier - Google Patents

Abstract

PURPOSE:To obtain stable charge potential by adopting a constant current power source for a power source to be connected to the conductive brush electrifier. CONSTITUTION:The constant current power source 3 is connected to the conductive brush electrifier 2 and specified current is passed to an electrostatic recording medium 1 via brush-like conductive fibers 2a. Since the current of this time is the charge quantity per unit time, the specified charge quantity per unit time is supplied to the surface of the electrostatic recording medium 1 with which the brush-like conductive fibers 2a are in contact. On the other hand, the electrostatic recording medium 1 moves at a uniform speed and, therefore, the region (a) of the specified area per unit time parts from the conductive fibers 2a. The specified charge quantity is eventually applied to the region (a) and the always equal charge potential is maintained. The stable electrification without having a potential fluctuation is executed in this way.

Description

[Detailed Description of the Invention] [Summary] A conductive brush charger having conductive fibers formed in a brush shape; a power source connected to the conductive brush charger to supply power to the conductive fibers; The purpose of the present invention is to provide a conductive brush charging device that is capable of stable charging without potential fluctuations due to changes in the environment, particularly humidity, and the power source is configured with a constant current power source, further comprising: The constant current power supply includes a power supply circuit that supplies current to the conductive brush charger, a detection circuit that detects the current value, and a comparison circuit that compares the detected current value with a reference value and outputs a difference signal. The device is configured to include a control circuit that controls the power supply circuit so that the difference signal becomes zero, and a removal circuit that removes a pulse-like component from the detected current value or the difference signal.

[Industrial application field]

The present invention relates to a charging device used for charging and neutralizing an electrostatic recording medium (photoreceptor, dielectric) in an image forming apparatus, such as an electrophotographic copying machine or an electrophotographic printer.
In particular, the present invention relates to a conductive brush charging device that includes at least a conductive brush charger having conductive fibers formed in a brush shape, and a power source connected to the conductive brush charger so as to supply power to the conductive fibers.

Image forming devices such as electrophotographic copying machines and electrophotographic printers are
With the demand for miniaturization, simplification, and cost reduction, there is a need for a charging method that is compact and has a simple configuration and can be charged at a low voltage.

BACKGROUND ART Conventionally, in electrophotographic copying machines, printers, and the like, a corona charging method is often used as a means for performing negative charging when forming an image on a photoreceptor or a dielectric electrostatic recording medium.

However, the corona charging method requires a high voltage of several kV for corona discharge, which increases the cost of the device, and the ozone generated by the discharge damages device components, shortening the lifespan of the recording medium in particular. There was a problem.

Furthermore, there is a problem that ozone causes discomfort to those who use the device, and when the concentration becomes high, it is harmful to the human body.

[Conventional technology]

In order to solve this problem, a charging method using a conductive brush that does not generate ozone, as shown in FIG. 19, has been proposed.

In this charging method, a conductive brush 2 to which a constant voltage 5 is applied is brought into contact with the electrostatic recording medium 1 to charge the electrostatic recording medium 1. By applying a constant voltage of 500 V-1. It is possible to charge the electrical recording medium l to a required potential.

However, this conductive brush charging method has a problem in that the charging potential on the electrostatic recording medium l varies greatly depending on the environment (ambient temperature, humidity).

In order to solve this problem of potential fluctuation, assuming that the cause of potential fluctuation is the fluctuation in the resistance value of the conductive fibers that make up the conductive brush 2, we applied water-repellent treatment to the conductive fibers to eliminate fluctuations in resistance due to humidity. method (Unexamined Japanese Patent Publication No. 56-147159)
(No. 46264/1983), or a method using artificial fibers with low hygroscopicity as the conductive fibers (Japanese Patent Laid-Open No. 57-46264) has been proposed.

[Problem that the invention seeks to solve]

However, merely stabilizing the resistance value of conventional conductive fibers does not eliminate potential fluctuations, and the problem of charging potential fluctuations still exists.

In particular, when trying to miniaturize the device, it is easiest to miniaturize the recording medium such as a photoreceptor, but at the same time, the process members disposed around it It is also necessary to reduce the length occupied by the storage device and the developing device in the circumferential direction of the recording medium.

Therefore, in this case, if the number of printouts per unit time is to be the same, the charging time on the recording medium by the charger must be shortened.

For this reason, in the case of a conventional constant voltage source, it is not possible to apply a so-called saturation charging method in which the charging time is sufficiently long to make the charging potential equal to the power supply voltage applied to the conductive fiber.

Therefore, when there is a change in the environment (particularly humidity), there is a problem in that the charged potential on the electrostatic recording medium fluctuates.

In view of these conventional problems, an object of the present invention is to provide a conductive brush charging device capable of stable charging without potential fluctuations in response to changes in the environment. An object of the present invention is to provide a conductive brush charging device that enables stable charging without potential fluctuations, even when charging must be carried out for such a short time that saturation charging cannot be applied.

[Means for solving problems]

FIG. 1 is a diagram illustrating the principle of a conductive brush charging device according to the present invention.

In the figure, 1 is an electrostatic recording medium on which engagement is performed, 2 is a conductive brush charger having conductive fibers 2a formed in a brush shape, and 3 is a constant current power source. It is connected to the conductive brush charger 2 so as to supply electric power to the conductive fibers 2a.

Further, the conductive brush charger 2 and the electrostatic recording medium 1 are provided so as to move relative to each other at a constant speed.

[For production]

As a result of a detailed study by the present inventors on the fluctuations in the charging potential depending on the environment of the conductive brush charging device, we found that the fluctuations in the charging potential on the electrostatic recording medium 1 are part of the charge transfer process during brush charging. We have found that this is due to fluctuations in the discharge stop voltage (dark value voltage of discharge) of aerial discharge.

Figure 2 shows the discharge stop voltage of the conductive brush charger.

FIG. 3 is a diagram showing the humidity dependence of charging potential, and shows an example in which the voltage applied by the charging voltage source is about 1.1 kV.

As shown in Figure 2, the discharge stop voltage of aerial discharge is:
It depends on the humidity, and as the humidity increases, the discharge stop voltage decreases.

By the way, in the brush charging method, if the difference between the charging potential on the electrostatic recording medium l and the voltage applied to the conductive fiber is equal to or higher than the discharge stop voltage, the discharge continues and charging is performed.

For this reason, when the discharge stop voltage decreases, charging progresses so that the difference between the charging potential and the potential of the conductive fiber becomes equal to the discharge stop voltage, and the charging potential increases when the humidity is low, as shown in Figure 2. higher than the case.

As explained above, the variation in the discharge stop voltage is the cause of the variation in the charging potential, so even if the variation in the resistance value of the conductive fiber is eliminated, the variation in the charging potential cannot be prevented under the application of a constant voltage.

In contrast, in the present invention, since the power source connected to the conductive brush charger 2 is a constant current power source 3, a constant electric charge can always be supplied to the surface of the electrostatic recording medium 1 in contact with the conductive fibers 2a. If the capacitance of the electrostatic recording medium l is approximately equal over the entire surface, the charging potential will be constant regardless of fluctuations in the discharge stop voltage.

That is, in the present invention, a constant current power source 3 is connected to the conductive brush charger 2, and a constant current is passed through the electrostatic recording medium 1 through the brush-like conductive fibers 2a.

At this time, since the current is the amount of charge per unit time, a constant amount of electricity 7Wi per unit time is supplied to the surface of the electrostatic recording medium 1 in contact with the brush-like conductive fibers 2a. There is.

On the other hand, since the electrostatic recording medium l is moving at a constant speed,
Since a region of a constant area ((a) in the figure) leaves the conductive fiber 2a per unit time, a constant amount of charge is given to the region (a), and the charging potential must always be equal. I can do it.

〔Example〕

Embodiments of the conductive brush charging device according to the present invention will be described in detail below with reference to the drawings.

(a) Description of one embodiment FIG. 3 is a diagram showing the overall configuration of a printer to which the conductive brush charger according to the present invention is applied, and shows a laser printer that prints on cut paper using an electrophotographic method. It is a diagram.

In the figure, 1O is a photosensitive drum, which is rotated at a constant speed in the direction of arrow A by a drive source (motor, gears, not shown) to repeatedly form a bond, and 20 is a conductive brush charger. Yes, 10 photosensitive drums
For uniformly charging the entire surface to a predetermined potential, 30
is a laser optical system, for example, a semiconductor laser diode is used as a light source, and a rotating polygon mirror (borigo, nmirror)
Information light is scanned and irradiated onto the photosensitive drum 10 at a constant speed using an R/θ lens and a semiconductor diode. 40 is a developing device that forms an electrostatic latent image on the drum 1O, in which a two-component developer consisting of toner and carrier is stored in a container 40a, and a magnetic brush is formed by a sleeve and a magnet roller 40b, and a photosensitive drum is formed. 5° is a paper cassette that converts the electrostatic latent image on the IO into a toner image. For example, a large number of A4 size papers 53 are stacked on a plate 51 and stored therein, as shown in FIG. 60 is a belt transfer device, in which sheets of paper 53 are sequentially fed out one sheet at a time by a half-moon-shaped pink roller 52 provided on the device side when loaded in the device casing 11, so that It is configured to transfer the toner image on the photosensitive drum 10 onto a sheet of paper using electrostatic force, and a drive motor (not shown) is configured to transport the sheet 53 from the position of the pink roller 52 to a fixing device 70, which will be described later. ,
Pulley 61.62. and a belt 63,
70 is a heat roller fixing device for fixing the toner image on the paper 53 by sandwiching the paper 53 between the heat roller 71 and the bank up roller 72;
5b is a paper discharge roller for discharging the paper 53 onto the stacker 76; 80 is a static eliminator, which is composed of a red LED that emits light with a wavelength of 660Ωm;
Something used to eliminate static from the photosensitive drum IO, 90
is a cleaner and uses a fur brush to clean the photosensitive drum l.
This is for collecting the toner remaining on the container 91 into the container 91.

FIG. 4 is a main part configuration diagram showing details of the photosensitive drum 10 and conductive brush charger 20 in FIG. 3. FIG.

In the figure, IO is a photosensitive drum, 20 is a conductive brush charger, and 3 is a constant current power source.

The photoreceptor drum IO includes a charge generating layer (CGL) 102. using a copper phthalocyanine-based organic photoconductor on an aluminum tube 101. It is a layered structure in which charge transport layers (CTL) 103 are sequentially applied and stacked, and is used for negative charging.

The conductive brush charger 20 has a conductive brush 22 made by weaving conductive fibers 221 in a pile shape fixed to a conductive substrate 21 made of a conductive material such as aluminum using a conductive adhesive 23. Configure.

This conductive fiber 221 is made of rayon fiber with conductivity imparted by uniformly dispersing carbon particles (Resoku manufactured by Unitika), the fiber thickness is 10 to 15 μm, and the resistance value is brush-like. It is selected to have a resistance of 103Ω per fiber.

Moreover, as this conductive fiber 221, "
Beltron (conductive nylon) can be used.

In the conductive brush 22, the aforementioned conductive fibers having a length of 5 mm are planted at a density of 155 fibers/1lIII2,
The width of the brush is 15-.

Then, the conductive brush charger 2o is connected parallel to the axial direction of the organic photosensitive drum IO, and the tip of the conductive brush 22 is connected for 0.5 s+ over the entire width of the organic photosensitive drum io in the width direction.
Attach so that they are in contact at about the same depth.

Further, a constant current power source 3 is connected to the conductive brush charger 20, and the organic photoreceptor drum IO is charged at a constant circumferential speed (60+u
By supplying current while rotating at +/s),
The organic photoreceptor drum IO is charged.

The constant current power supply 3 has the ability to flow a constant current to the connected external circuit (conductive substrate 21), and the output current is between 0 and 3.
Any value of -20 μA can be selected, and the output voltage range is 0 to -2 kV.

As this constant current power supply 3, one having a circuit configuration as shown in the block diagram of FIG. 5 can be used.

In the figure, a high voltage power supply circuit 305 is for providing a constant current output to the conductive brush charger 20, a current detection circuit 301 is for detecting the output current value of this high voltage power supply circuit 305, and a reference current signal generator. The circuit 302 generates a reference value set so that the output current value of the high-voltage power supply circuit 305 becomes a predetermined value, and the comparison circuit 303 generates a reference value from the reference current signal generation circuit 302. The control circuit 304 compares the detection outputs of the current detection circuit 301 and outputs a difference signal, and the control circuit 304 controls the high voltage power supply circuit 305 according to the difference signal from the comparison circuit 303 so that the difference between the two becomes zero. For example,
This is shown in Publication No. 345 and the like.

In the configuration described above, the organic photoreceptor drum 10 was charged under different environmental conditions and the surface potential was measured using a surface electrometer. The measurement results are shown in FIGS. 6 and 7.

In the figure, graph (a) represents the charging potential under environmental conditions of a temperature of 25° C. and a humidity of 50% RH. In addition, in graph (b), the temperature is 5℃ and the humidity is 20%R.
H, Graph (C) shows a temperature of 35℃ and a humidity of 80%RH.
In graph +d), the temperature is 35° C. and the humidity is 30% RH.

Note that FIG. 6 shows the measurement results when the charging time was 250 ms, and FIG. 7 shows the measurement results when the charging time was 100 ms.

As is clear from FIGS. 6 and 7, even if the output current of the constant current power supply 3 is changed from -6 to -18 μA, the difference in band it in each graph (a) to (d) is At most tOV
There are only degrees, from low temperature and low humidity (graph (b)) to high temperature,
A stable charging potential with no fluctuation was obtained over high temperatures (graph (C)).

Furthermore, even if the charging time is shortened, the charging potential is about several tens of degrees Celsius because the charging process (charge injection process) in which the charge is directly transferred from the conductive fiber 221 to the organic photoreceptor 10 is reduced. However, it is not affected by changes in the charged potential due to the environment.

FIG. 8 is a diagram showing the results of charging using the conductive brush charger 20 and organic photoreceptor drum 10 configured as described above, using the power supply as a constant voltage source, and measuring the surface potential with a surface electrometer. .

The environmental conditions for each graph (a) to (d) are as shown in Figures 6 and 7.
It is similar to the one shown in the figure.

As is clear from FIG. 8, in the conventional device, the charging potential of the organic photoreceptor drum lO decreases from 150 to 2 due to environmental changes.
It fluctuates by about 00V.

Therefore, as shown in graph (C), when the charging potential becomes high, carrier adhesion occurs in printers that use a reversal phenomenon such as laser printers, and the adhesion between the drum and the paper deteriorates during transfer. , transcription omissions occur. Additionally, the drum may be mechanically damaged by the spilled carrier.

On the other hand, when the charging potential becomes low as shown in graph (b), fogging occurs in the background area.

As explained above, in this example, when the charging time is relatively short, the charging potential does not change significantly even if environmental changes occur (and stable charging is possible). Become.

(bl Other Embodiments As mentioned above, by using the constant current power supply shown in FIG. 5 as the power supply connected to the conductive brush charger 20, it is possible to suppress fluctuations in the charging potential of the photoreceptor drum. It becomes possible.

However, with the constant current power supply shown in FIG. 5, a problem occurs in the photosensitive drum 10 where pinholes, which are defects in the photosensitive layer, exist.

That is, in the pinhole area, the organic photoconductor layer 1
02 and 103 are missing, and the aluminum drum 101, which is the base material of the photosensitive drum 1O, is exposed.

Therefore, when the conductive brush 22 comes into contact with this pinhole part, a short circuit occurs, and the current driving the conductive brush charger 20 flows through the entire pinhole part, and the photoreceptor drum IO is no longer charged. .

The block diagram shown in FIG. 9 is a diagram showing a constant current circuit that solves the above problem.

In the figure, the difference from the constant current circuit shown in FIG. 5 is that a pulse removal circuit 306 is provided between the current detection circuit 301 and the comparison circuit 303.

The operation of the circuit will be explained below.

When the conductive fibers 221 of the conductive brush 22 come into contact with the pinholes, a short circuit occurs and an excessive current flows.

Here, since the photoreceptor drum 10 is rotating at a constant speed, the time during which the conductive brush 22 and the pinhole are in contact is determined by the width of the conductive brush 22 and the circumferential speed of the photoreceptor drum 10.
Usually, it is several 100m5 or less.

Therefore, when the conductive fiber 221 comes into contact with the pinhole, the pulse width is several hundred meters in the current detection circuit 301.
An excessive current waveform of 5 or less is detected.

In conventional constant current circuits, control is performed based on this current waveform, so control is performed in the direction of reducing the current.
The output voltage of the high voltage power supply circuit 305 decreases, and charging becomes impossible.

However, in the constant current circuit of this embodiment, the excessive current waveform with a pulse width of several hundred m5 is removed by the pulse removal circuit 306, so that it does not appear in the signal input to the comparison circuit 303.

Therefore, the output of the high voltage power supply circuit 305 is
The voltage before the contact between 2 and the pinhole is maintained, and charging becomes possible.

FIG. 10 is a diagram showing an example of a known low-pass filter circuit showing the internal configuration of this pulse removal circuit 306.

The cutoff frequency f (see FIG. 11) of this low-pass filter circuit is expressed as: "=□ 2πCAR However, R+ = Rz = RCz = C+ / 2.

FIG. 12 shows a more detailed block diagram of the constant current circuit of this embodiment.

In the figure, the current flowing through the conductive brush charger 20 is detected as a voltage value by a resistor R3 that constitutes a current detector 301. The detection voltage is amplified by AMPI, and the first
The signal is input to the low-pass filter shown in the θ diagram. Here, the pulsed detection signal is cut off.

The output of this low-pass filter is input to the inverting input terminal of operational amplifier OP2 via resistor R5.

The voltage determined by the variable resistor R7 and the resistor R8 that constitute the reference current signal generation circuit 302 is input to the non-inverting input terminal of the operational amplifier OP2 that constitutes the comparison circuit 303, and is compared with the output of the filter, and the difference is calculated. R6/R
The signal is multiplied by 5 and output from operational amplifier OP2.

After this signal is amplified by AMP2, the control circuit 3
The signal is manually inputted to the transmission circuit Q1 that constitutes 04. Transmission circuit Q
The output of AMP2 increases or decreases in response to the signal of AMP2.

The output of the oscillation circuit Ql is connected to the primary side of the high voltage transformer TI constituting the high voltage power supply circuit 305, and a high voltage is generated on the secondary side in response to the signal of AMP2. The secondary output of the high voltage transformer TI is rectified by a diode D, a capacitor C3, and a resistor R4, converted to a DC voltage, and applied to the conductive brush charger 20.

In this way, in this constant current circuit, the conductive brush charger 2
Since the current flowing through the conductive brush charger 20 is controlled to be equal to a predetermined value by the resistors R7 and R8, a constant current is always passed through the conductive brush charger 20.

Moreover, since the pulsed current detection signal is blocked by the filter, it does not affect the control signal, and the output voltage remains constant during the short period when the brush and pinhole are in contact, and charging is performed. be exposed.

In this embodiment, a low-pass filter that is a pulse removal circuit 306 is provided between the current detection circuit 301 and the comparison circuit 303, but a low-pass filter that is a pulse removal circuit is provided after the comparison circuit 303, and the reference signal It is also possible to remove a pulse-like signal included in the difference signal.

Further, in this embodiment, a low-pass filter is used as the pulse removal circuit, but the present invention is not limited to this, and it goes without saying that any circuit having a function of removing pulses can be applied.

However, because an excessive current flows through the brush, which is a conductive fiber that comes into contact with a pinhole that is a defective part of the organic photoreceptor, the conductive fibers may be burned out or the organic photoreceptor may be damaged. was there.

Combustion of conductive fibers causes melting and burning of the photosensitive layer,
The substrate of the photoreceptor is further exposed.

Since the exposed substrate is a conductor, the area where the short circuit occurs will gradually expand, potentially causing serious and permanent damage to both the photoreceptor and the conductive brush.

Therefore, in this embodiment, as shown in FIG. 13, the resistance value Rh of the conductive fiber 221 and the conductive fiber 22
The resistance value Rb is set so that the current value (2) flowing through the conductive fiber 221 determined by the applied voltage Va from the high voltage source 3 to
Alternatively, the applied voltage Va is determined.

In addition, in the charging model of the conductive brush charging device shown in FIG. 13(a) and the equivalent circuit shown in FIG. 13(b), Va is the high voltage a.
3, Rb is the resistance of the conductive fiber 221, Rc is the contact resistance between the conductive fiber 221 and the dielectric on the surface of the photoreceptor 10, and Cc is the adjacent conductive fiber 221 at the contact portion.
, Cd is the capacitance of the photoreceptor, ■ is the conductive wire m22
is the current flowing through 1.

In this way, the conductive fibers 221 have the desired resistance value Rh at the applied voltage Va of the conductive brush charger, and the current value determined by the applied voltage and the resistance value is below the limit current value, so if the photoreceptor Even if the conductive fibers come into contact with the base IO, the electric current () flowing through the fibers 221 is limited by the resistance value Rb of the conductive wires w1221 themselves, so it is possible to prevent burnout due to short circuits.

Here, the relationship between the resistance value of the conductive fiber 221, the applied voltage, and the limiting current will be explained.

In order to find out the limiting current, the applied voltage was gradually increased for conductive rayon fibers (pile length 5+++s) having various resistance values, and the current value at which the fibers were burned out (limiting current) was measured.

For each fiber, the applied voltage Va that was burnt out and the time,
The current 1b flowing through the fiber is indicated by O in FIG. 14.

The measurement results are normalized to a thickness of 1 denier and a length of 1-. However, 1 denier is a unit expressing the thickness of a fiber, and the thickness of a fiber that is 9000 m long and weighs 1 g is called 1 denier.

As is clear from Fig. 14, the conditions under which the fibers are burnt out regardless of the resistance value of the fibers are the applied voltage Va and the limiting current 1
In the relationship of b, Va·1b=P (P is constant).

The solid line in FIG. 14 represents the relationship Va-'I=4 mW, and it can be seen that it agrees well with the measurement results. Similarly, the broken line in the figure represents the relationship Va·I=2 mW. Anticipating variations in fiber resistance 1iff221,
With some margin, the above relationship Va・I=2mW is
Practically speaking, it is preferable to set the upper limit so that burnout does not occur.

Thereby, by determining the resistance value of the fiber so that the relationship between the applied voltage Va and the current I flowing through the fiber satisfies Va-1≦2mW, burning out of the fiber can be prevented.

In other words, the conductive fibers constituting the conductive brush charger are
Even when the fiber contacts the photoreceptor base, which is a conductor, the current flowing through the fibers is suppressed to below the limit current by the resistance of the fibers themselves, so that burning does not occur and irreparable damage to the photoreceptor does not occur.

The upper limit of the voltage applied to the conductive brush charging device to obtain the charging potential necessary for the recording process of the electrophotographic printer shown in FIG. 3 is usually about 1500V.

Assuming Va=1500V, calculating the resistance value that satisfies the conditions of Va-1≦2mW, the thickness is 1 denier and the length is ll.
It becomes 4.5X per l11, 10'Ω or more.

In addition, in FIG. 14, the data for hair length 5Il- is
Since it is normalized to Il, assuming that the resistance value is uniform,
The applied voltage Va in FIG. 14 is the actual applied voltage of 115.

On the other hand, conductive fibers with excessive resistance result in a decrease in charging potential. However, if the resistance value of the fiber is 1 denier and 1Q13Ω or less per length lll1l, there is almost no decrease in the charging potential.

FIG. 15 is a diagram showing the relationship between the resistance value and charging potential of conductive fibers.

In FIG. 15, in the equivalent circuit shown in FIG. 13(b), the resistance value R of conductive tam per 1 denier and l++s
The results are shown in which h is calculated as 0Ω and 1013Ω +QI4Ω. In addition, as other values, standard values in actual charging were adopted. - By way of example, Cd=
1.0/JF/la", Cc=0.2μF/a", Rc
= 300Ω.

As is clear from FIG. 15, when the resistance value is Q13Ω, the charging potential shows a change that is almost the same as when the resistance value is OΩ.

However, when the resistance value is 1014Ω, the charging potential changes slowly and the potential decreases.

In view of the above points, a brush was manufactured from conductive rayon fiber with a thickness of 6 denier and a length of 5 mm, with a resistance value of 4.5XlO' to 1OI:IΩ per 1 denier thickness and 1 mm length. When recording was performed using the electrophotographic printer shown in FIG. 3, stable recording was possible without any damage to the photoreceptor even if a short circuit occurred.

(C1 Another Example) By the way, as a result of further experiments, the conductive brush charging method shown in FIGS.

The charged potential on the electrostatic recording medium 10 may fluctuate in environments such as humidity, particularly in high humidity.

The cause of this is that the surface resistance of the support member (polyamide resin (nylon), ABS resin, acrylic resin, etc.) that holds the conductive fibers in contact with the surface of the electrostatic recording medium decreases due to high humidity, and the current It turned out that this was due to a leak. In the constant current charging method, a constant current of several 10μ is passed through the conductive fiber for charging, but since the current is the amount of charge per unit time, the surface of the recording medium in contact with the fiber has a constant charge per unit time. quantity is supplied and the charging potentials are always equal. If the above-mentioned leak occurs at this time, the current that should charge the electrostatic recording medium escapes through the support member, making it impossible to charge the electrostatic recording medium, resulting in a potential drop.

For this reason, in this example, as shown in FIG. 16, the support member is formed of a resin with good moisture absorption properties that does not reduce the resistance value even in high humidity, and the surface resistance of the support member is to prevent charge leakage.

In FIG. 16, a conductive brush charger 432 connects a brush 441a woven with conductive fibers 441 to a conductive adhesive 44.
2 to a conductive substrate 443 made of aluminum or the like, and a supporting member 444 is attached to the substrate 443. Conductive fiber 441 is made of rayon fiber with conductivity imparted by uniformly dispersing carbon particles, and the fiber thickness is selected to be 10-15 μm in diameter and the resistance value to be 109Ω per fiber. . and length 5
The brush 441a is constructed by flocking fibers 441 with a density of 155/am". The width of the brush 441a is 15 mm.
+am. The support member 444 is made of a resin with good moisture absorbing properties that does not reduce the resistance value even in high humidity. This resin is a fluororesin (typically tetrafluoroethylene (PTFE)).

Examples include epoxy resin and silicone resin. This support member 444 is attached to the frame 445 of the apparatus, and in this state, the conductive brush charger 432 is parallel to the axis of the photoreceptor drum 431, and the conductive fibers 441 are approximately 0.
It is in contact with the photosensitive drum 431 at a depth of 5 mm. The conductive brush charger 432 configured as described above constitutes a conductive brush charging device 447 together with a constant current power source 446 connected to the conductive brush charger 432 so as to supply constant power to the conductive fibers 441.

In this conductive brush charging device, the support member 444 is made of a resin with good moisture absorption properties, so the surface resistance of the support member 444 is maintained high even in high humidity, and leakage of charge can be prevented. Therefore, charging can be performed without reducing the charging potential. This effect is clear from the graph of FIG. 17, which was measured using a surface electrometer. Figure 17 shows the relationship between current value and charging potential during charging. Graph (a) shows the charging potential under standard conditions of temperature 25°C and humidity 50% RH. Charging potential in RH environment is shown respectively.Graphs (al,
(The difference in bl was at most about IOV, confirming the above effect.

FIG. 18 shows a modification of the embodiment shown in FIG. 16.

The conductive brush charging device of this example includes a conductive brush charger in which brush-shaped conductive fibers are directly held on a support member.

FIG. 18 is a side view showing the structure of the conductive brush charging device of this example, and in the figure, 461 is a conductive brush charging device equipped with a conductive brush charger 462 and a constant current power source 446.

The conductive brush charger 462 has a brush 441a attached to a support member 463 using a conductive adhesive 442 and held therein. The support member 463 is made of aluminum or the like, and its surface is coated with a resin layer 464 made of epoxy resin with a thickness of 50 μm.

In the case of this example, the resin layer 464 prevents charge leakage, and the same effect as the previous example can be obtained, and furthermore, it can be applied to conventional devices as is. In addition, this example requires less resin than the previous example, which is advantageous in terms of cost.

(dl Other Examples In the examples described above, an organic photoreceptor was used as the photoreceptor.
It is also advantageous for selenium-based photoreceptors and a-Si-based photoreceptors.

In addition, the shape is not limited to drums, but also film-like,
A belt-like object may also be used. Furthermore, as a brush charger,
Needless to say, it is also effective to use a brush roller with a brush attached to a rotating shaft and charge the brush by bringing it into contact with the brush while rotating.

〔Effect of the invention〕

As explained above, in the present invention, since the power supply connected to the conductive brush charger is a constant current power supply, a constant amount of charge can always be supplied to the electrostatic recording medium without being affected by environmental conditions. , a stable charging potential can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a diagram explaining the principle of the conductive brush charging device according to the present invention, Fig. 2 is a diagram showing the humidity dependence of the discharge stop voltage and the charging potential, and Fig. 3 is a diagram showing the humidity dependence of the conductive brush charging device according to the present invention. Figure 4 is a diagram showing the overall configuration of the printer, Figure 4 is a diagram showing the details of the photosensitive drum and conductive brush charging device, Figure 5 is a block diagram showing the circuit configuration of the constant current power supply, Figures 6 and 4 are diagrams showing the overall configuration of the printer. Figure 7 is a diagram showing the relationship between current value and charging potential, Figure 8 is a diagram showing the relationship between applied voltage and charging potential, Figure 9 is a block diagram showing the circuit configuration of another constant current power supply, and Figure 10 is a diagram showing the relationship between applied voltage and charging potential. Diagram 11 showing the internal configuration of the pulse removal circuit
The figure shows the cut-off frequency characteristics, and Figure 12 is a detailed circuit diagram showing the configuration of another constant current power supply.
fa), (#) 131D is a diagram showing the principle configuration of a conductive brush charging device, Figure 14 is a diagram showing the relationship between applied voltage Va and limiting current 1b, and Figure 15 is a diagram showing the resistance value and charging of conductive fibers. FIG. 16 is a side view showing the structure of a conductive brush charging device according to another embodiment of the present invention; FIG. 17 is a diagram illustrating the effects of another embodiment; FIG. 18 is another embodiment FIG. 19 is a side view showing a modification of the example, and FIG. 19 is an explanatory diagram of the prior art. In the figure, 2 is a conductive brush charger, 2a is a conductive fiber, 3 is a constant current power supply, 301 is a current detection circuit, 303 is a comparison circuit, 304 is a control circuit, 305 is a power supply circuit, 306
is a pulse removal circuit.

Claims (3)

[Claims] (1) a conductive brush charger (2) having conductive fibers (2a) formed in a brush shape; and a conductive brush charger (2) configured to supply power to the conductive fibers (2a). A conductive brush charging device comprising at least a connected power source (3), wherein the power source (3) is a constant current power source. (2) The constant current power supply includes a power supply circuit (305) that supplies current to the conductive brush charger (2), a detection circuit (301) that detects the current value, and a reference for the detected current value. a comparison circuit (303) that compares the detected current value and outputs a difference signal; a control circuit (304) that controls the power supply circuit (305) so that the difference signal becomes zero; The conductive brush charging device according to claim 1, further comprising a removal circuit (306) for removing a pulse-like component from the difference signal. (3) The conductive brush charger is composed of a support member (444) holding conductive fibers (2a) formed in a brush shape, and at least the surface of the support member (444) is Claim (1) or (1) characterized in that it is formed of a resin with good moisture absorption properties that does not reduce resistance.
2) The conductive brush charging device described above.