JPH06250506A - Developing device - Google Patents

Abstract

PURPOSE:To suppress the discharge to a photosensitive drum even if an electrically conductive foreign matter is mixed in a developing device of an image forming device. CONSTITUTION:A developing sleeve 26 is composed of a magnet body 26A, a sleeve 26B fitted on the outside and a high resistance layer 26C to cover the outer peripheral surface of the sleeve 26B. A condition of developing bias 27 impressed between the developing sleeve 26 and a photosensitive drum 3 is set to be (E=2X10<6>-6X10<6>V/m and FAC=4-20kHz). Provided that, E is electric field strength between the photosensitive drum and the developing sleeve, and (fAC) is a frequency.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a means for suppressing discharge to a photoconductor drum caused by a conductive foreign substance mixed in a developing device of an electrophotographic image forming apparatus such as a copying machine or a printer.

[0002]

2. Description of the Related Art Generally, an electrophotographic image forming apparatus such as a copying machine is composed of a platen on which a document is placed, a document irradiation lamp reciprocating below the platen, a reflection mirror, and a fixed projection lens and a reflection mirror. Scanning optical system, a photosensitive drum which is charged with a predetermined potential by a band electrode and rotates, and toner is applied to the electrostatic latent image formed on the surface of the photosensitive drum by the scanning optical system to develop the electrostatic latent image. A developing device, and a transfer pole that transfers a toner image onto a recording paper surface that is a transfer material that is conveyed below the surface of the photosensitive drum,
It is composed of a separating electrode and a removing electrode, a fixing device for fixing the toner image transferred onto the surface of the recording paper, and a cleaning device for removing toner, paper dust, etc. remaining on the surface of the photoconductor after the transfer. ing.

Then, desired toner images are successively recorded on the surface of the recording paper which is intermittently conveyed along a predetermined conveying path.

The developing sleeve, which is a developer carrying member provided in the developing device, rotates with a gap of about 500 μm from the peripheral surface of the photosensitive drum. An alternating bias is applied between the photosensitive drum and the developing sleeve so that the developer on the developing sleeve adheres to the electrostatic latent image formed on the peripheral surface of the photosensitive drum to develop the latent image.

[0005]

Generally, the outer circumference of the developing sleeve is made of a conductive stainless steel (SUS) material. Then, a foreign substance such as metal which is a conductive substance is sometimes mixed in the developer in the developing device. When the foreign substance reaches between the developing sleeve and the photoconductor drum, the developing electric field causes discharge from the tip of the foreign substance. As a result of this discharge, the charging potential of the opposing photoconductor drum is erased and toner adheres, causing a ring-shaped image defect in the image region of the photoconductor drum. Since this image defect is recorded on the transfer material, the image quality is significantly deteriorated.

The present invention solves such a problem and suppresses discharge due to foreign matter even if conductive foreign matter enters the developing device and reaches between the developing sleeve and the photosensitive drum. An object of the present invention is to provide a developing device in which an image defect does not occur on the body drum.

[0007]

[Means for Solving the Problems]
It is achieved by any one of b, c and d.

(A) Development in which an alternating bias is applied between a developer carrier and a latent image carrier having an electrostatic latent image to apply the developer on the developer carrier to form a visible image In the apparatus, a high resistance material is provided on the surface of the developer carrying member, and the alternating bias is set to the following condition.

E = 2 × 10 ^{6 to} 6 × 10 ⁶ V / m f _AC = 4 to 20 kHz, where E is the electric field strength between the latent image carrier and the developer carrier.

F _AC is the frequency.

(B) A developing device as described in the item (a), wherein a magnetic rod is used as the developer conveying means.

(C) A developing device as described in the item (a), wherein a magnetic developer and inter-electrode development are used.

(D) A developing device as described in the item (a), wherein a magnetic developer and a magnetic rod are used.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention is a side sectional view showing the structure and arrangement of a developing sleeve in FIG. 1, a potential difference formed on a photosensitive drum in FIG. 2, and a developing device in FIG. A side sectional view showing the configuration and a side sectional view showing the configuration of the image forming apparatus in FIG. 4 will be described.

However, the present invention is not limited to this embodiment.

As shown in FIG. 4, an electrophotographic image forming apparatus (hereinafter simply referred to as an image forming apparatus) 18 is provided with a platen glass P for placing a document M on the upper surface of the main body 1, and the platen glass P in the main body 1 is provided. A scanning optical device 2 is provided below. The scanning optical device 2 comprises a reciprocating document irradiation lamp 2a, a first mirror 2b, second and third mirrors 2c forming a V shape, a fixed projection lens 2d and a fourth mirror 2e. A photoconductor drum 3 is rotatably provided in the center of the main body 1 in the direction of the arrow, and a belt electrode 4 for uniformly charging the photoconductor 3a along the rotation direction is provided around the photoconductor drum 3, and a toner replenishing device. 5, the toner is replenished with toner, the developing device 6 having a developing sleeve 6a therein, and the transfer electrode 7
, Separation electrode 8, static elimination electrode 9, and cleaning device 10
And are arranged in sequence. Two kinds of recording papers of different sizes are housed in the paper feed cassettes 11 and 11 'and set in the main body 1. Reference numeral 12 denotes a first paper feed roller that feeds the recording paper stored in the paper feed cassette 11 to a standby position before the second paper feed roller 13, and a belt is provided to prevent double feeding of the recording paper. It is composed of rotating rollers 12a, 12a and a stop roller (also referred to as a separating roller) 12b. Reference numeral 13 is an appropriate timing so that the recording paper fed by the first paper feed roller 12 is temporarily stopped at the standby position, and then the front end of the visible image on the photoconductor 3a and the front end of the recording paper are aligned at the transfer position. The second paper feed roller 14 that feeds paper again toward the transfer position at 14 is a guide plate for guiding the recording paper fed by the first paper feed roller 12 to the position of the second paper feed roller 13, It is opened and closed by operating a lever (not shown) so that the jammed paper can be taken out by inserting a hand. Reference numeral 15 denotes a conveying device that conveys the recording sheet after transfer to the fixing position, and the fixing device 16 includes a heating roller 16a and a pressure roller 16b. Reference numeral 17 denotes a paper discharge roller that discharges the recording paper after fixing to the outside of the main body.

When the copy button is operated in the above apparatus, the original M on the platen glass P is exposed and scanned by the scanning optical device 2, and an electrostatic latent image of the original M is formed on the photoconductor 3a of the photoconductor drum 3. It This electrostatic latent image is made into a visible image by the developing device 6, and this visible image is transferred by the transfer electrode 7 to the recording paper fed from one of the paper feed cassettes 11 and 11 'of the main body 1. After the transfer, the recording paper is separated from the photoconductor 3a by the separation electrode 8, is conveyed to the fixing device 16 by the conveying device 15, is fixed there, and is ejected by the ejection roller 17. In this way, desired toner images are successively recorded on the recording paper surface.

Next, the developing device 6 will be described with reference to FIG.

FIG. 3 is a cross-sectional view of the main part of the developing device 6 provided in the image forming device 18. Reference numeral 20 is the developing device main body forming the housing of the developing device 6, 22 is a first stirring member, and 23 is a second stirring member. A member, 24 a supply roller, 26 a developing sleeve, 28 a magnetic rod which is a developer thin layer forming member having rigidity to regulate the amount of the developer applied to the peripheral surface of the developing sleeve 26, 28a
Is a spring plate for regulating the amount of developer conveyed, and is a magnetic rod.
28 is pressed against the developing sleeve 26 with a constant load in the absence of developer. Reference numeral 27 is a scraper for cutting the spikes of the developer, 25 is a stirring partition plate, and 21 is an upper lid integrally attached to the upper surface of the developing device main body.

The toner replenished in the developing device 6 is sufficiently agitated and mixed with the carrier by the second stirring member 23 rotating in the direction of the arrow and the first stirring member 22 rotating so as to overlap each other in the opposite direction. The developer D, which is the above-mentioned magnetic developer, is sent to the developing sleeve 26 via the supply roller 24 and the magnetic rod 28.

The first stirring member 22 and the second stirring member 23 are screw-shaped members having a spiral angle of left-handed rotation in opposite arrow directions and are conveyed to the inner side by the thrust of the first stirring member 22. The toner and the carrier successively pass over the stirring partition plate 25 whose upper edge is slanted downward in the direction toward the back of the drawing, and the second
It moves to the side of the stirring member 23 and is conveyed to the front side of the drawing by its thrust, and becomes a homogeneous developer D that is triboelectrically charged by the mixing action of the toner and the carrier during that time, and is a sponge-like supply roller that rotates in the arrow direction The toner is adhered in a layered manner on the peripheral surface of the developing sleeve 26 which rotates clockwise by the arrow 24.

Then, the toner conveyed by the developing sleeve 26 is added to the electrostatic latent image formed on the peripheral surface of the photosensitive drum 3 adjacent to the surface of the developing sleeve 26 with a predetermined gap, so that a toner image is formed. Is developed. The rotations of the first and second stirring members 22, 23, the supply roller 24, and the developing sleeve 26 are transmitted to each other by a drive transmission mechanism mounted on the side surface of the developing device main body 20.

Next, the means for suppressing the discharge of the conductive foreign matter mixed in the developing device 6 of the present invention will be described with reference to FIGS. 1 and 2.

As shown in FIG. 1, the developing sleeve 26 has a magnet body 26A in which a plurality of N and S magnetic poles are fixed in the circumferential direction, and a sleeve 26B having a conductive property made of a stainless steel material on the outside thereof. Is fitted. The outer surface of the sleeve 26B is coated with a high resistance layer 26C having a thickness of 5 to 20 μm made of, for example, phosphazene resin.
The resistance value of the high resistance layer 26C is set in the range of 10 ⁶ to 10 ¹⁰ Ω. In addition to the above phosphanezen resin, a ceramic resin, a fluorine resin or a polycarbonate resin may be used.

A developing bias 27 is connected to the developing sleeve 26 thus constructed, as shown in the figure. 27A of the developing bias 27 generates an oscillating electric field between the photosensitive drum 3 to the base portion by applying an AC bias voltage (V _AC) to the developing sleeve 26 through the safety resistor 27C in the AC bias power source is grounded As a result, toner transfer control from the developer D layer to the photosensitive drum 3 in the developing area is performed.

27B is a DC bias power source, which is superposed on the _AC bias voltage (VAC) and is superimposed on the DC bias voltage ( _VDC ).
Is applied to attach the toner on the peripheral surface of the developing sleeve 26 to the electrostatic latent image formed on the peripheral surface of the photosensitive drum 3.

As shown in the figure, the peripheral surface of the photosensitive drum 3,
The gap d from the peripheral surface of the developing sleeve 26 is set in the range of 400 to 700 μm, preferably 500 μm so that the development can be performed by non-contact. In this way, the inter-electrode development with the magnetic developer D is performed.

The AC bias voltage V _AC of the developing bias 27 is preferably in the range of 1.5 to 3.5 KV, preferably 2.8 KV, and the DC bias voltage V _DC is in the range of -300 to -800 V, preferably -500 V, and the frequency f _AC. Is set in the range of 4 to 20 KHz, preferably 5 to 10 KHz. Then, as shown in FIG. 2, a potential difference ΔV is formed between the charging potential V _H of the photosensitive drum 3 charged by the band electrode 4 and the exposure potential V _L exposed by the scanning optical device 2.
For example, the charging potential V _H is −650 V and the exposure potential V _L is −5.
Each is set to 0V.

Then, the electric field strength E between the photosensitive drum 3 which is an image carrier and the developing sleeve 26 which is a developer carrier.
Is represented by E = ΔV / d.

In the present invention, the value of E, which is the condition of the developing bias 27, is 2 × 10 ^{6 to} 6 × 10 ⁶ V / m, preferably 2.6 × 10 ^{6 to} 4.0.
Set within the range of × 10 ⁶ V / m. The preferable frequency at this time is in the range of 5 to 10 kHz as described above. The resistance value of the photosensitive layer 3a of the photosensitive drum 3 made of, for example, OPC (organic semiconductor) is set in the range of 10 ¹³ to 10 ¹⁵ Ωcm.

By the developing sleeve 26 coated with the high resistance layer 26C in this way, even if the conductive foreign matter m such as metal is mixed in the developing device 6 at the position shown in FIG.
The discharge from the foreign matter m is suppressed by the
Also, the above-mentioned ring-shaped image defect does not occur without erasing the electrostatic charge. Further, even if the discharge is generated, it is suppressed, so that it does not become a large defect that disturbs a normal image. Although the present invention has been described by taking a mono-black image forming apparatus as an example, it is of course applicable to a color image forming apparatus.

[0032]

The high resistance layer is provided on the outer peripheral surface of the developing sleeve according to the present invention, and the alternating bias condition is set, so that conductive foreign matter such as metal is mixed in the developing device, and the photosensitive drum and the developing sleeve are separated from each other. Since the discharge due to the foreign matter is suppressed even when it reaches during the time period, a normal image is always recorded on the transfer material without causing a defect in the toner image formed on the peripheral surface of the photosensitive drum. .

[Brief description of drawings]

FIG. 1 is a side sectional view showing the structure and arrangement of a developing sleeve according to an embodiment of the present invention.

FIG. 2 is a diagram showing a potential difference formed on a photosensitive drum.

FIG. 3 is a side sectional view showing a configuration of a developing device.

FIG. 4 is a side sectional view showing the configuration of the image forming apparatus.

[Explanation of symbols]

 3 Photosensitive drum 6 Development device 18 Image forming device 26 Development sleeve 26A Magnet body 26B Sleeve 26C High resistance layer 27 Development bias 27A AC bias power supply 27B DC bias power supply 28 Magnetic rod D Developer (magnetic developer) d Gap m Foreign matter

Claims (4)

[Claims] 1. A developing device which applies an alternating bias between a developer carrier and a latent image carrier having an electrostatic latent image to apply the developer on the developer carrier to form a visible image. 2. A developing device, wherein a high resistance substance is provided on the surface of the developer carrier, and the alternating bias is set to the following condition. E = 2 × 10 ^{6 to} 6 × 10 ⁶ V / m f _AC = 4 to 20 kHz, where E is the electric field strength between the latent image carrier and the developer carrier.
f _AC is the frequency. 2. The developing device according to claim 1, wherein a magnetic rod is used as the developer transporting means. 3. The developing device according to claim 1, wherein a magnetic developer and inter-electrode development are used. 4. The developing device according to claim 1, wherein a magnetic developer and a magnetic rod are used.