JP2595976B2 - Conductive brush charging device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] The present invention relates to a conductive brush charging device for charging a photoreceptor, and relates to burnout of a conductive fiber that occurs during an electric short circuit state when the conductive fiber comes into contact with a defective portion existing on the photoreceptor. The current flowing through the conductive fiber, which is determined by the resistance value of the conductive fiber and the voltage applied to the conductive brush charging device, is equal to or less than the limit current for burning out the conductive fiber.

[Industrial applications]

The present invention relates to a charging device, and more particularly to a conductive brush charging device used for charging and removing a photosensitive member in an electrophotographic copying machine and a printer.

With the demand for simplification, low cost, and maintenance-free copiers and printers, the use of inexpensive organic photoconductors that are non-toxic and user-replaceable has increased, and the use of inexpensive organic photoconductors has increased. And a stable charging device has been required.

[Conventional technology]

Conventionally, Se-based photoconductors have been used as photoconductors for electrophotographic copying machines and printers. However, the Se-based photoreceptor has to collect the used photoreceptor due to the problem of toxicity. Therefore, the photoreceptor cannot be replaced by a user and requires maintenance by specialized personnel.

To solve this problem, there has been provided a simple and inexpensive electrophotographic apparatus which uses a non-toxic organic photoreceptor and does not require maintenance of specialized personnel. However, there is a problem that the organic photoreceptor is easily oxidized and deteriorated when exposed to ozone. The corona charger is used exclusively for charging the organic photoreceptor, but the corona charger generates ozone during corona discharge.

Further, the thickness of the organic photoreceptor is 10 to 15 μm, which is thinner than that of several tens of μm of the Se-based photoreceptor, and has a large capacity, requiring a large amount of current for charging. This is also a factor that increases the amount of generated ozone.

In particular, most of organic photoconductors currently in practical use are charged with negative polarity, and corona discharge of a page generates a larger amount of ozone than positive polarity.

On the other hand, a method using a conductive brush has been proposed as a charging method that does not generate ozone instead of corona charging.

In the present charging method, charging is performed by bringing a conductive brush to which a voltage is applied into contact with the surface of a dielectric, and charging can be performed with a low applied voltage of 500 V to 1.5 kV, and there is an advantage that ozone is not generated.

[Problems to be solved by the invention]

However, when the present charging method is applied to an organic photoreceptor, an electrically short-circuit is caused by the conductive fiber constituting the brush contacting a defective portion existing in the organic photoreceptor, and an excessive current flows in the short-circuited portion. There has been a problem that the conductive fibers are burned out and the organic photoreceptor is damaged.

Burning out of the conductive fibers causes melting and burning of the photosensitive layer, exposing the substrate of the photoreceptor.

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

Normally, since a power supply has a built-in means for limiting overcurrent, when a short circuit occurs, no voltage is applied and charging is not performed. For this reason, a large disqualification occurs in the output image. That is, it is often used in copying machines,
In the recording process of the positive exposure and the normal development, a band-shaped white spot occurs, and in the process of the negative exposure and the reversal development often used in a printer, a band-shaped solid black area is generated.

The organic photoreceptor forms a photosensitive layer exclusively by coating. For this reason, a region that is electrically weak (a region with a low dielectric strength) is likely to be generated due to mixing of air ducts and air bubbles. At present, it is very difficult to manufacture an organic photoreceptor having no such defects, and it is necessary to consider the presence of defects before using an organic photoreceptor.

For this reason, a conductive brush charging device capable of performing stable charging is required regardless of the presence of a region having a low dielectric strength in the photosensitive layer.

SUMMARY OF THE INVENTION In view of the above-described conventional problems, an object of the present invention is to reduce the quality of an output image, and to reduce the conductivity that occurs when an electrically short-circuit occurs when a conductive fiber comes into contact with a defective portion existing on a photoconductor. It is an object of the present invention to provide a conductive brush charging device capable of preventing burning of fibers.

[Means for solving the problem]

The purpose of the present invention is to provide a conductive brush charging device for charging a photoreceptor 11 with a conductive brush 3 including a conductive fiber 3a, as shown in FIG.
Rb, the relationship between the current value I flowing through the conductive fiber 3a determined by the voltage Va applied to the conductive fiber 3a, the fiber length of the conductive fiber 3a 1mm, Va · I per 1 denier thickness Va · I ≤ In order to satisfy the condition of 2 mW, the resistance value Rb of the conductive fiber 3a is 4.5 mm per fiber length 1 mm and thickness 1 denier of the conductive fiber 3a.
This is achieved by a conductive brush charging device, which is set to 10 ⁷ to 10 ¹³ Ω.

That is, FIG. 1A shows a charging model of the conductive brush charging device, and FIG. 1B is an equivalent circuit of FIG. 1A, where Va is the applied voltage of the high voltage source 4. , Rb is the resistance of the conductive fiber 3a, Rc is the contact resistance between the conductive fiber 3a and the dielectric on the surface of the photoconductor 11, Cc is the capacitance of the conductive fiber 3a close to the contact portion, and Cd is the Capacity, I is conductive fiber
This is the current flowing through 3a.

(Operation)

As described above, the conductive fiber 3a has a desired resistance value Rb at the applied voltage Va of the conductive brush charger, and the current value determined by the applied voltage and the resistance value is equal to or less than the limit current value. Even if the conductive fiber comes into contact with the photoreceptor substrate 11, the resistance of the conductive fiber 3a itself, the fiber 3a
Is limited, so that burnout due to a short circuit can be prevented.

〔Example〕

Hereinafter, embodiments of the conductive brush charging device according to the present invention will be described in detail with reference to the drawings.

FIG. 2 is a configuration diagram of an electrophotographic recording system using a conductive brush charging device.

In the figure, 1 is an organic photosensitive drum, 20 is a conductive brush charger, which is composed of a substrate 2 and a brush-like conductive fiber 3a, which is connected to a high voltage source (not shown) via a contact, and the fiber 3a Is applied with a voltage. 5 is an LED for image exposure
An array, 6 is a rod lens array, 7 is a developing machine, 8 is a transfer belt, 9 is a fixing device, 10 is a cleaner, and 12 is a light source for static elimination.

The organic photosensitive drum 1 is uniformly charged by the conductive brush charger 20, and a latent image is formed by an image exposure system including the LED array 5 and the rod lens array 6. Thereafter, toner is adhered to the latent image by the developing device 7 to obtain a visible image.

Next, the image is transferred to the recording paper 13 by the transfer belt 8, fixed by the fixing device 9, and the image is fixed on the recording paper 13. The toner remaining on the drum without being transferred is removed by the cleaner 10.

The substrate 2 is made of aluminum and has a brush processed into a curved surface along the drum surface. The brush-like conductive fibers 3a were manufactured by weaving rayon in which carbon was dispersed in a pile shape. This was fixed to the substrate 2 with a conductive adhesive.

The voltage is applied to the substrate 2 by a power supply unit (not shown).

The conductive brush charger is used by being fixed in a state of uniformly contacting the surface of the organic photoreceptor.

Here, the relationship between the resistance value of the conductive fiber 3a, the applied voltage, and the limit current will be described.

In order to know the limit current, the voltage was gradually increased by applying voltage to conductive rayon fibers (hair length 5 mm) having various resistance values, and the current value (limit current) when the fibers were burned out was measured.

For each fiber, the applied voltage Va that was burned out and at that time,
The current Ib flowing through the fiber is shown in FIG.

The measurement results are shown normalized to a thickness of 1 denier and a length of 1 mm. However, 1 denier is a unit representing the thickness of the fiber, and the thickness of a fiber having a length of 9000 m and weighing 1 g is called 1 denier.

As is clear from FIG. 3, regardless of the resistance value of the fiber, the condition under which the fiber is burned out is Va · Ib = P (P: constant) in the relationship between the applied voltage Va and the limit current Ib.

The solid line in FIG. 3 represents the relationship of Va · I = 4 mW, and it can be seen that the measured value is in good agreement with the measurement result. Similarly,
The relationship of Va · I = 2 mW is shown by the broken line in the figure. Anticipate the variation of the resistance value 3a of the fiber, give some margin,
It is practically preferable to set the relationship of Va · I = 2 mW as the upper limit at which burning does not occur.

Thus, by determining the resistance value of the fiber such that the relationship between the applied voltage Va and the current I flowing through the fiber satisfies Va · I ≦ 2 mW, burning of the fiber is prevented.

That is, even if the conductive fibers constituting the charging brush charger are in contact with the photosensitive body which is a conductor, the current flowing due to the resistance of the fibers themselves is suppressed to the limit current or less,
No burning occurs and no irreparable damage occurs to the photoconductor.

The upper limit of the voltage applied to the conductive brush charging device for obtaining the charging potential required for the recording process of the electrophotographic printer in FIG. 2 is usually about 1500 V.

Calculating a resistance value that satisfies the condition of Va · I ≦ 2 mW with Va = 1500 V gives 4.5 × 10 ⁷ Ω or more per 1 denier thickness and 1 mm length.

In FIG. 3, since the data of the hair length of 5 mm is normalized to 1 mm, when the resistance value is considered to be uniform, the applied voltage Va in FIG. 3 is 1/5 of the actual applied voltage.

On the other hand, a conductive fiber having an excessive resistance causes a decrease in the charged potential. However, if the resistance value of the fiber is 1 denier and 10 ¹³ Ω or less per 1 mm length, there is almost no decrease in the charging potential.

FIG. 4 is a diagram showing the relationship between the resistance value of the conductive fiber and the charging potential.

In FIG. 4, in the equivalent circuit shown in FIG.
The resistance Rb of the conductive fiber per 1 denier and 1 mm is set to 0Ω,
The calculation results are shown as 10 ¹³ Ω and 10 ¹⁴ Ω. still,
As other values, standard values in actual charging were adopted. As an example, Cd = 1.0 μF / m ² , Cc = 0.2 μF / m
² , Rc = 300KΩ.

As is clear from FIG. 4, when the resistance value is 10 ¹³ Ω, the change in the charging potential is almost the same as that when the resistance value is 0 Ω.

However, when the resistance value is 10 ¹⁴ Ω, the change in the charging potential becomes slow, and the potential drops.

In view of the above, the resistance per 1 mm thick and 1 mm length is 4.5 × 10 ⁷ to 10 ¹³ Ω, 6 denier thick and 5 m long
A brush is made of conductive rayon fiber of
When recording was performed using the electrophotographic printer shown in the figure, even if a short-circuit condition occurred, the photosensitive member was not damaged and stable recording was possible.

〔The invention's effect〕

As described above, according to the present invention, even when the photosensitive member has a defect, the current is limited by the resistance of the conductive fiber itself, so that the fiber does not burn out.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining the principle of the present invention, FIG. 2 is a diagram showing the configuration of a recording apparatus, FIG. 3 is a diagram showing the relationship between an applied voltage and a limiting current, and FIG. FIG. In the figure, 3a is a conductive fiber, 4 is a high voltage source, 11 is a photoconductor, Rb
Denotes a resistance value, I denotes a current, and Va denotes an applied voltage.

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-61-57954 (JP, A) JP-A-62-207178 (JP, A)

Claims (1)

(57) [Claims] 1. A conductive brush (3) containing conductive fibers (3a).
A conductive brush charging device for charging the photoreceptor (11) by the following method, wherein the resistance (Rb) of the conductive fiber (3a) and the voltage (Va) applied to the conductive fiber (3a) are determined. The relationship between the current value (I) flowing through the conductive fiber (3a) and the fiber length (1 mm) of the conductive fiber (3a) is Va · I ≦ 2 mW per denier.
The conductive fiber (3a) should have a resistance value (Rb) of 4.5 × 10 ⁷ -10 ¹³ Ω per 1 denier fiber length and 1 denier thickness so as to satisfy the following conditions. A conductive brush charging device, characterized in that: