JPS62108264A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent a carrier from sticking to a photosensitive body and damaging the photosensitive body while a device is held stopped by turning off primary electrostatic charge and impressing the DC component of a developing bias to the photosensitive body before the passage of the part of the photosensitive body which is not subjected to the primary electrostatic charge through a developing device. CONSTITUTION:The primary electrostatic charge is turned off and the DC component of the developing bias is turned off upon arrival of the region where the surface potential of the photosensitive drum 3 attains V1 by receiving electrostatic charge for transfer at the developing position; therefore, the DC component of the developing bias is kept impressed to the drum 3 until the region thereof subjected to the primary electrostatic charge passes the developing position. The potential difference between the surface potential of the drum 3 and the surface potential of the developing sleeve of the developing device is prevented from attaining the value at which the carrier charged to a positive polarity in the developer sticks to the photosensitive drum or above. The sticking of the carrier onto the drum 3 is thus prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an electrophotographic image forming apparatus employing a so-called reversal development method.

(Prior Art) Conventionally, an image is created by scanning an electrophotographic photoreceptor with a beam of light modulated in accordance with a recorded image signal using a laser, a light emitting diode array, or a liquid crystal shutter array.
1; In a printer that prints images, the image scanning method that develops the photoreceptor portion exposed by the 1-light distribution flux is 1E.
It is a flow. but.

In this case, the area to be developed is the exposed area and has a lower potential than the area that is not developed. This method of developing the light potential VL portion that has been exposed to low potential and not developing the dark potential VO portion that is not exposed is called a reversal development method. In this reversal development method, development is performed using toner with the same polarity as the primary charging potential of the photoreceptor (that is, toner charged to the same polarity as VO), so the developing bias of the developing device is set to the same polarity as the photoreceptor. Therefore, the potential is much lower than the dark potential Vo. Further, as a developing device, one employing a jumping developing method 7 using a -component magnetic toner is used.

On the other hand, in forming an image, after image exposure is performed on a photoconductor which has been uniformly (+F) charged by negative order charging,
This exposed portion is reversely developed by a developing device to which a predetermined developing bias is applied. This developed image is transferred from the photoreceptor onto a transfer paper by a transfer charger and then discharged. Note that the toner remaining on the photoreceptor is cleaned by a cleaning device consisting of a plate or the like. Thereafter, the secondary charging, developing bias, and transfer charging are simultaneously turned off, the photoreceptor rotates a predetermined number of times, and the apparatus stops.

However, in this case, the developing device uses a one-component magnetic toner as a developer, and since the toner contains a black magnetic material, the color development of color toner is poor, and the demand for multicolor toner is increasing recently. There is a problem that it cannot be used for image formation.

In order to solve this problem, it is conceivable to use a developing device that employs a magnetic brush development method using a two-component developer consisting of powdered magnetic carrier and toner as a developer. In this development method, powdered magnetic carrier is magnetically held in a brush shape around a developing electrode to form a magnetic brush, and powdered toner is brought into contact with the magnetic brush, and the powdered toner is magnetically charged by frictional electrification. Attach it to the brush. The electrostatic layer image on the surface of the photoreceptor is developed using powdered toner deposited on a magnetic brush, and as a matter of course, the carrier and toner (same polarity as the negative charge) have opposite polarities. (tF electricity is flowing.

In this case, since it is not necessary to use a magnetic toner as the toner, the color toner has good color development, and since the carrier serves as a developing electrode, it has excellent gradation.

(Problem to be Solved by the Invention) However, in the case of such a prior art, since the -th charge and the developing bias are turned off at the same time after the image forming process, the second charge is turned off when the -th charge is turned off. Although the area located between the primary charger and the developing device of the photoreceptor L is negatively charged, the developing device has a developing bias that has the same polarity as the primary charging and is lower than this. Not applied.

Therefore, the primary voltage acts directly on the magnetic carriers having the opposite polarity to the negative charge, and the magnetic carriers adhere to the above region on the photoreceptor. The magnetic carrier attached to the surface of the photoreceptor is
When passing through a cleaning device that cleans the surface of the photoreceptor with a blade or the like, there is a problem in that the surface of the photoreceptor is damaged and the charging characteristics of the photoreceptor are changed, leading to deterioration of the image formed. Further, the toner is inadvertently consumed together with the magnetic carrier, resulting in wear and tear.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and its purpose is to provide an image forming installation that employs a single reversal developing force type, and furthermore, uses toner and carrier as a developing device. An object of the present invention is to provide an image forming apparatus in which carrier does not adhere to a photoreceptor even when a two-component developer is used.

(Means for Solving the Problems) In order to achieve the above object, the present invention uses a reversal development method in which toner is attached to the exposed portion of a photoreceptor, and furthermore, a developing device uses the toner as a developer and a magnetic material. In an image forming apparatus that performs magnetic brush development using a carrier, when the apparatus stops operating, the primary charging is first turned off, and the developing bias is turned off after the non-primarily charged portion of the photoreceptor passes through the developing device. It is configured as follows.

(Example) The present invention will be explained below based on illustrated embodiments.

FIG. 1 shows a sectional view of a main body of a laser beam printer as an embodiment of an image forming apparatus according to the present invention.
In the figure, l is a scanner unit consisting of a semiconductor laser and a polygon mirror shade, and the laser beam emitted from the semiconductor laser and modulated in accordance with the recorded image signal is rotated in the direction of the arrow by the polygon mirror rotating at high speed. The electrophotographic photosensitive drum 3.1: is repeatedly scanned. 2 is an f-0 lens that focuses the laser beam onto the drum 3F, and 2' is a folding mirror that directs the laser beam onto the drum 3. What is the semiconductor laser used in this device?

The wavelength is 770 to 800 nm, and the photosensitive drum uses a photosensitive member 1 sensitive to this wavelength, such as a phthalocyanine-based organic photoconductor, an amorphous silicon-based photoconductor, or a selenium-based photoconductor.

Reference numeral 4 denotes, for example, a negative primary charger, which uniformly charges the photosensitive drum 3E coated with the photosensitive member with a primary charge (that is, photosensitization) of about -400 to -500. This-
The photosensitive drum 3 negatively charged by the charger 4 is scanned by the laser beam described above, and an electrostatic Wi image is formed. The bright part V of this electrostatic latent image is -50 to -1
00V, dark areas as non-image areas -400 to -500V
becomes.

In this embodiment, the portion to be visualized is scanned with a laser beam. That is, the portion irradiated with the laser beam is developed. It uses a so-called image scan method.

This electrostatic latent image is visualized by the primary developing device 5 using negatively charged toner. The developing device 5 employs a magnetic brush developing method.

In this developing method, a powder magnetic carrier is magnetically held in a brush shape around the developing sleeve 5' to form a magnetic brush, and by bringing the toner into contact with the magnetic plan, the toner is magnetically charged by frictional electrification. Attach it to the brush.

The electrostatic latent image on the surface of the photoreceptor is developed using toner attached to a magnetic brush, and the carrier is naturally charged with a positive polarity opposite to that of the toner. The sleeve 5' that carries and conveys the toner of this developing device becomes a developing electrode, and a DC voltage of -300 V is superimposed as a developing bias voltage by a power source (not shown).
An alternating current voltage of V, p, IK)lz is applied. The DC voltage component of the developing bias voltage has a value between the potential of ■ and the potential of Vo, but in any case, by applying the developing bias to the developing electrode.

As is well known, a fog-free and edge-effect free image can be obtained.

On the other hand, the transfer sheet P on the stacking table S is fed onto the drum 3 by a feed roller 6 and a registration roller 7 that rotates in synchronization with the image on the photosensitive drum 3. Then, the toner image on the photosensitive drum 3L is transferred to a transfer charger 8 having a positive polarity, which is opposite to that of the negative charger 4.
The image is transferred onto the sheet P. After that, the sheet P separated from the drum 3 by the separating means 9a is guided to the fixing device IO by the guide 9. After the toner image on the sheet P is fixed, the sheet P is discharged onto the tray 12 by the discharge roller 11. On the other hand, the toner remaining on the photosensitive drum 3 after the transfer is removed by the cleaner 13.

FIG. 2 shows changes in the surface potential of the photosensitive drum during one image forming process.

FIG. 3 shows a timing chart of the primary charger, transfer charger, and laser beam. In the line showing the operating state of each means, a low level part is OFF and a high level part is ON.In the pre-rotation process, at the same time as the rotation of the photosensitive drum starts, the DC component of the developing bias is applied and the -forming charger is turned on. starts. The transfer charger starts operating after the primary charger starts operating.

This is because the polarity of the transfer charger is positive, so if the charge is applied to the portion of the photosensitive drum that has not been primarily charged, charging memory remains on the photosensitive drum. . Therefore, after the photosensitive drum is primarily charged, transfer charging is started to overlap the portions that have received this secondary charge. In this way, the potential of the photosensitive drum L is set to a high potential with the opposite polarity to the negative charge (i' is not charged, and no charging memory is left on the drum.
In this way, during the pre-rotation, the photosensitive drum is rotated one or more revolutions, thereby stabilizing the sensitivity of the photosensitive drum.

After the pre-rotation, an image forming process is performed. In this image forming step, image exposure is performed with a laser modulated by the recorded image signal, and an electrostatic latent image is formed as described above.
This latent image is developed and the toner image is transferred to a transfer sheet. The image forming process ends when the toner image transfer to the transfer sheet is completed, and then the post-rotation step F is executed and the apparatus is stopped.

In this post-rotation step when the apparatus is stopped, the primary charger continues discharging for a predetermined time after the image forming process F is completed, and then first only the primary charging is turned off. Turning off this negative charge
After a time tl, the DC component of the developing bias is turned off, and after a time t2, the transfer charging is turned off. tl is the time required for the leading end of the area where the primary charging is 0FFL and the potential is Vl to reach the developing sleeve 5' position of the developing device 5, and t2 is the time required for the leading end of the area where the potential of the photosensitive drum is 0FFL to reach the position of the developing sleeve 5' of the developing device 5; This is the time required to reach the previous position.

As mentioned above, firstly, the primary charging is turned off, and the area where the surface potential of the photosensitive drum becomes vT due to transfer charging is
When reaching the development position, the DC component of the development bias is turned off.
F, the DC component of the development bias is applied until the primary charged area of the photosensitive drum passes the development position. Therefore, the potential difference between the surface potential of the photosensitive drum and the developing sleeve of the developing device is the value at which the positively charged carrier in the developer adheres to the photosensitive drum (
200V or higher), and the carrier does not adhere to the photosensitive drum.

Furthermore, since the transfer charging is turned off immediately before the area of the surface potential VT of the photosensitive drum reaches the transfer charger, when the area of the surface potential V of the photosensitive drum reaches the development position, the DC voltage of the developing bias Even if a small amount of toner is left on the photosensitive drum until the component is turned off, this toner is removed by the cleaner 13 without being transferred to the transfer charger 8. Therefore, the toner is not transferred to the transfer charger 8. It is possible to prevent the particles from adhering to each other and causing charging unevenness 7.

On the other hand, the AC component of the developing bias and the rotation of the developing sleeve are turned on depending on the developing timing.

OFF is performed. The AC component of this developing bias is O
N and OFF are performed to prevent the toner from scattering, and turning ON and OFF of the rotation of the developing sleeve is performed to prevent the toner and carrier from scattering and their deterioration.

Further, at the start of operation of the apparatus, carrier adhesion can be prevented by turning on the direct IR component of the developing bias at the same time as the -order charging. Also, at the start of the loading operation, the rotation of the developing sleeve and the adjustment of the developing bias must be adjusted. i
, the component is turned off, so that the area of the photosensitive drum is uncharged.

Toner adhesion when passing through the development position can be suppressed to a minimum. Furthermore, when the surface of the photosensitive drum to which the toner has adhered passes through the transfer charger, it is desirable to turn off the transfer charge, and by doing so, it is possible to prevent toner from adhering to the transfer charger.

(Effects of the Invention) The present invention has the above-described structure and operation, and when the device stops operating, the primary charging is first turned off, and after the non-primarily charged portion of the photoreceptor passes through the developing device, the primary charging is turned off. Since the development bias was turned off, a magnetic brush development method using a two-component developer of toner and carrier was adopted as the development device, and a reversal development method was adopted that improved the color development and gradation properties of color toner. In the apparatus, it is possible to prevent the carrier from adhering to the photoreceptor and damaging the photoreceptor when the apparatus is stopped.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing a laser beam printer as an embodiment of an image forming apparatus according to the present invention, FIG. 2 is a graph showing changes in the surface potential of a photosensitive tram, and FIG. 3 is a timing diagram of the laser beam printer. It is. Explanation of symbols

Claims (1)

[Claims] In an image forming apparatus that uses a reversal development method in which toner is attached to the exposed portion of a photoreceptor, and in which a developing device performs magnetic brush development using the toner and a magnetic carrier as a developer, when the apparatus stops operating, first the primary charging is performed. OFF
An image forming apparatus characterized in that the developing bias is turned off after a portion of the photoreceptor that is not primarily charged passes through a developing device.