JPH08123149A - Brush electrifying device - Google Patents

Abstract

PURPOSE: To prevent the occurrence of the irregularity of an image due to the pin hole of a latent image carrier, to prevent the pin hole from being enlarged, and to eliminate the limitation of a brush material by specifying the drooping power characteristic of the current and the voltage of a power source in the case of electrification. CONSTITUTION: As to this brush electrifying device 1 having a brush in contact with a photoreceptor 3 and the power source 12 by which a DC voltage is applied on the brush; a specified voltage is kept in the case the drooping power characteristic of the current and the voltage of the power source 2 is <=20μA, and the drooping curve of the current and the voltage of the power source 2 passes through an area where electric power is >=45mW and <=108mW in the case the drooping power characteristic is >=20μA. When the drooping curve of the current and the voltage of the power source 12 by which the DC voltage is applied on the brush in contact with the photoreceptor 3 is in the area where the power is >=45mW and <=108mW, the pin hole exists on the photoreceptor 3, the lowering of the current and the voltage of the power source is small so as not to lower the potential of the photoreceptor 3 even though an excessive current flows between the pin hole and the brush, so that belt-like horizontal black stripe does not appear on an image. The brush is moderately melt by the current flowing between the pin hole and the brush, so that the pin hole is closed without being enlarged.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charger used in an image forming apparatus such as a printer, a facsimile or a copying machine which uses an electrophotographic process.

[0002]

2. Description of the Related Art When using a brush charger that contacts a photosensitive member, which is a latent image carrier, and charges it by applying a voltage, a small-area conductive portion or low resistance portion called a pinhole is formed on the surface of the photosensitive member. If there is, a dielectric breakdown occurs between the brush that is in contact with the pinhole and an overcurrent flows through the pinhole, and while the pinhole portion is in contact with the brush charger, it is not charged, and a band-shaped black appears on the image. Solid portions (horizontal black stripes) may occur, or pinholes may become larger.

As means for solving this problem, conventionally, a method of lowering the initial charging potential of the photoconductor, a method of increasing the film thickness of the photosensitive layer, a method of incorporating an overload protection circuit in the power supply and limiting the output current, a power supply. There is a method of inserting a protective resistance between the brush and the metal substrate of the brush charging device.

[0004]

In the means of the prior art, the method of lowering the initial charging potential of the photoconductor and the method of increasing the film pressure of the photoconductor include pinholes and the like which are stochastically generated in the photoconductor manufacturing process. It is ineffective against defects and does not provide an essential solution to the problem. Also, by incorporating an overload protection circuit in the power supply, the overcurrent that flows through the pinhole is limited to prevent expansion of the pinhole to prevent damage to the photoconductor, or a protective resistance is provided between the power supply and the metal substrate of the brush charger. The way to put in and limit the current is when the current limiting function works,
The potential of the metal substrate of the brush charging device is lowered, and the potential of the entire region where the contact of the brush charging device is in contact is lowered. As a result, band-shaped horizontal black stripes occur at the points where pinholes exist on the image.

Further, as described in JP-A-62-207178, it is possible to eliminate the effect of pinholes by a method of defining the resistance value of the conductive fiber of the brush, but the material of the brush is limited. There is a problem that will be done.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a brush charger which does not cause image drooling due to a pinhole in a latent image carrier, prevents the pinhole from expanding, and does not limit the brush material. To provide.

Therefore, in order to achieve the above object, the brush charger of the present invention is a brush charger comprising a brush that contacts the latent image carrier and a power supply that applies a DC voltage to the brush. The characteristic of the power supply is that the current and voltage of the power supply during charging is in the range of 45 mW or more and 108 mW or less. Further, the brush may be rayon yarn that has been subjected to flame retardant treatment.

[0008]

The current and voltage decay curve of the power source for applying the DC voltage to the brush contacting the latent image carrier has a power of 45 mW or more,
In the range of 108 mW or less, there is a pinhole in the latent image carrier, and even if an overcurrent flows between the pinhole and the brush, the power voltage of the power source does not decrease so much and the potential of the latent image carrier does not decrease. Therefore, the band-shaped horizontal black stripes do not appear in the image. Further, the current flowing between the pinhole and the brush has an effect of appropriately melting the brush and closing the pinhole without expanding it.

[0009]

Embodiments of the present invention will now be described with reference to the drawings.

FIG. 1 is a vertical sectional view of an electrophotographic cartridge using the charging brush of the present invention. In the figure, the electrophotographic cartridge includes a charger 1, a photoconductor 3 which is a latent image carrier, a toner carrier 4, a supply roller 5, a regulating blade 6, a toner 7, a stirring member 8, and a toner hopper. 9 and a cleaner 10. A direct current voltage is applied to the charger 1 by the power supply 12 to cause an OPC (Organic Photoconduct) on the aluminum base tube.
or), Se-based photosensitive film 3 having a photosensitive film formed thereon is uniformly charged, and an initial potential is applied to the outer peripheral surface thereof. The aluminum base tube of the photoconductor 3 is grounded or given a low level potential. Exposure of image data 2 is performed on the surface of the photoconductor 3 from a light source such as a laser, an LED or a liquid crystal (not shown) to form an electrostatic latent image.

The toner 7 as a developer is guided by a stirring member 8 to a supply roller 5 made of a conductive or insulative urethane or silicone foam, aluminum or the like, and is made of silicone rubber, urethane rubber or nitrile butylene rubber. , A natural rubber, or a toner carrier 4 made of a flexible material such as urethane or silicon foam or a member obtained by subjecting this to a surface treatment.

The toner 7 guided to the toner carrier 4 is regulated by a regulating blade 6 composed of a spring member made of metal such as stainless steel, phosphor bronze, nickel silver, etc., and is formed into a uniform thin layer. At this time, the toner 7 is charged by friction. A voltage having the same polarity as that of the toner 7 is applied to the toner carrier 4, and the charged thin-layer toner 7 on the toner carrier 4 is applied to the photoconductor 3 by the electric field when facing the photoconductor 3. 3 is adhered to the electrostatic latent image on 3 and developed, and a toner image is formed.

The toner image on the photoconductor 3 is transferred to a recording medium such as paper, OHP, and postcard by a transfer unit (not shown), and the toner image on the recording medium is fixed on the recording medium by a fixing unit (not shown) to form an image. obtain.

The brush charger 1 has the structure shown in FIG. 2, and the brush 1A has a bundle of 100,000 F / 96 F (filament) of conductive acrylic fibers having a thickness of 6.2 denier.
It consists of the ones planted in the base cloth 1B with the density of inch ² .
The base cloth 1B is a conductive substrate 1D with a conductive double-sided tape 1C.
Fixed to. The length L, width W, and height H of the brush 1A are
L = 132 mm, W = 6 mm, H = 5 mm. The height H of the brush 1A includes the thickness of the base cloth 1B and the conductive double-sided tape 1C. The brush fibers used are polyprene,
Synthetic fibers such as rayon, nylon, polyester, polycarbonate and polyvinyl alcohol fibers may be used. The conductive substrate 1D can be made of metal such as stainless steel, iron, copper, aluminum, or semiconductive engineer plastic.

(Embodiment 1) Falling power characteristics of FIG. 3 (hereinafter,
A voltage of -1315V is applied by a power source 12 of P1 to a brush 1A made of flame-retarded rayon yarn having a yarn resistance value of 10 ⁶ Ω · cm, and a photoconductor 3 having a pinhole exists. Was charged, and a white solid image and a halftone dot image were printed by the process described above. The output voltage and current of the power source 12 change according to the impedance change between the photoconductor 3 and the brush 1A during charging. The decline characteristic is
The output characteristics of the power supply 12 due to the impedance change are shown. In the decay characteristic P1 of the first embodiment, the specified voltage (-1315V) is maintained at 20 μA or less and the power passes through the region between 45 mW and 108 mW at 20 μA or more.

(Embodiment 2) A power supply 1 having a decay characteristic P2 shown in FIG.
The thread resistance value is 10 ⁶ Ω · c at -1350 V
By applying to the brush 1A made of m-ray flame-retarded rayon yarn, the photoconductor 3 having pinholes was charged, and the whole white solid image and the whole halftone dot image were printed by the process described above. With the decay characteristic P2, the specified potential is maintained up to 60 μA, and the current limiter is applied at 60 μA. That is, the power supply 12 has a current limiter circuit that applies a limiter at 60 μA. This is the embodiment of claim 3.

(Comparative Example 1) A power source 1 having a decline characteristic P3 shown in FIG.
The thread resistance value is 10 ⁶ Ω · c at -1350 V
m of flame-retarded rayon yarn was applied to charge the photoconductor 3 having pinholes, and a full-white solid image and a full-dot image were printed by the process described above. In the decay characteristic P3, the specified potential is maintained up to 20 μA, but the region does not pass through the region where the power is 45 mW or more.

(Comparative Example 2) A power source 1 having a decline characteristic P4 shown in FIG.
The thread resistance value is 10 ⁶ Ω · c at -1350 V
m of flame-retarded rayon yarn was applied to charge the photoconductor 3 having pinholes, and a full-white solid image and a full-dot image were printed by the process described above. In the decline characteristic P4, the power when the current limit is reached exceeds 108 mW.

(Results) Example 1, Example 2, Comparative Example 1,
Table 1 shows the results of the white solid image on the entire surface, the halftone dot image on the entire surface, and the degree of pinhole expansion during running in Comparative Example 2.

[0020]

[Table 1]

If the current and voltage decay characteristics do not pass through a region of 45 mW or more as in Comparative Example 1, the voltage effect becomes large and band-shaped horizontal black stripes occur. Further, the current value flowing into the pinhole is small and the pinhole is not enlarged, but since the effect of melting the brush and closing the pinhole is small, it takes time for the band-shaped horizontal black stripes to disappear by running.

When the decay curve of current and voltage passes through the region of 108 mW or more as in Comparative Example 2, the voltage effect is reduced and strip-shaped horizontal black stripes are eliminated, but the energy when the current flows into the pinhole is reduced. It's too big to enlarge the pinhole. As you continue running, the voltage effect increases and strip-shaped horizontal black stripes occur.

Therefore, when the decay curve of current and voltage is 20 μA or less as in the first and second embodiments, the specified voltage is maintained,
At 20 μA or more, when passing through the region of electric power of 45 mW or more and 108 mW or less, the voltage effect is small and the band-shaped horizontal black stripes do not occur. Further, since the energy when the current flows into the pinhole is moderate, the effect of melting the brush and closing the pinhole is high, and the pinhole is not enlarged.

[0024]

As described in detail above, according to the present invention, the characteristic of current and voltage decay from the power source for supplying the DC voltage to the brush of the brush charger keeps the specified voltage at 20 μA or less.
At 0 μA or more, by passing through the area of electric power of 45 mW or more and 108 mW or less, the pinholes on the latent image carrier disappear, black streaks are prevented, the halftone dot image recording density becomes uniform, and the pinholes have a large energy. , The pinhole does not expand. In addition, the material of the brush is not limited, and the flexibility of selecting the brush is large.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of an electrophotographic cartridge using a brush charger according to an exemplary embodiment of the present invention.

FIG. 2 is a perspective view of a charger showing an embodiment of the present invention.

FIG. 3 is a graph of current and voltage decay curves of the power supply according to the first embodiment of the present invention.

FIG. 4 is a graph of current and voltage decay curves of a power supply showing a second embodiment of the present invention.

FIG. 5 is a graph of current and voltage decay curves of a power supply showing a first comparative example of the present invention.

FIG. 6 is a graph of current and voltage decay curves of a power supply showing a second comparative example of the present invention.

[Explanation of symbols]

 1 Brush Charger 1A Brush 1B Base Fabric 1C Conductive Double-sided Table 1D Conductive Substrate 2 Exposure 3 Photoconductor 4 Toner Carrier 5 Supply Roller 6 Regulation Blade 7 Toner 8 Stirring Member 9 Toner Hopper 10 Cleaner 11 Shutter 12 Power Supply

Claims (3)

[Claims] 1. A brush charger having a brush in contact with a latent image carrier and a power source for applying a DC voltage to the brush, the current and voltage of the power source having a decaying power characteristic of 20 μA.
Below is the specified voltage, and above 20μA is 45m.
A brush charger which passes a region of W or more and 108 mW or less. 2. The brush charger according to claim 1, wherein the brush is made of flame-retarded rayon yarn. 3. The brush charger according to claim 1, wherein the power source has a current limiter circuit that limits a current when supplying power in the area.