JPS6139669B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a photoreceptor cleaning method.

A so-called visible image transfer type copying device, that is, an electrostatic latent image is formed on a photoreceptor, this is developed to obtain a visible image on the photoreceptor, and this visible image is transferred onto a recording sheet. In this type of copying apparatus, the same photoreceptor is used repeatedly, so the toner remaining on the photoreceptor after the visible image is transferred is removed before a new electrostatic latent image is formed. A cleaning step is required to remove it from the photoreceptor.

Various methods for cleaning the photoconductor have been considered depending on the development method, but the magnetic brush development method is one in which a developer formed by mixing a magnetic carrier and a charged toner is magnetically held and developed. and forming a magnetic brush in the developing section,
In a method in which the tip of a magnetic brush is brought into contact with the surface of a photoreceptor in a developing section, and toner is applied to the electrostatic latent image from the tip through electrostatic interaction between the toner and the electrostatic latent image to perform development. A method of cleaning a photoreceptor using a magnetic brush itself is known. That is, during cleaning, the tip of the magnetic brush rubs the surface of the photoconductor, and the toner remaining on the photoconductor is caught by the tip and removed from the surface of the photoconductor. By doing so, there is no need to provide a dedicated photoreceptor cleaning device, and the structure of the copying apparatus can be simplified.

However, this photoreceptor cleaning method has a problem in that the cleaning effect depends on the toner concentration in the magnetic brush.

That is, if the toner concentration in the magnetic brush that contacts the surface of the photoreceptor during cleaning is high, a sufficient cleaning effect cannot be obtained; on the other hand, if the toner concentration is low, the photoreceptor cannot be cleaned effectively. It is. On the other hand, however, if we look at this from the perspective of the development effect, a toner concentration in the magnetic brush that is low enough to be effective in cleaning the photoconductor causes a lack of image density in the copied image.

Conventionally, in order to solve this problem, a bias voltage was applied to the magnetic brush holder during cleaning, and such a bias voltage was
Methods such as switching between developing and cleaning, or providing a separate magnetic brush for cleaning have been proposed, but these methods have drawbacks such as lack of effectiveness and complication of equipment. .

The purpose of the present invention is to eliminate the above-mentioned drawbacks and propose a method for cleaning a photoreceptor, which can effectively clean the photoreceptor using a magnetic brush without impairing the developing effect, and which can be carried out using a device with a simple structure. It is to be.

The present invention will be described below with reference to the drawings.
FIG. 1 is a diagram schematically showing only the main parts of a magnetic brush developing device, which is an example of a device for carrying out the present invention. That is, in FIG. 1, numeral 1 is a photoreceptor, numeral 2 is a developer tank, numeral 3 is a sleeve,
Code 4 is hopper, code 5 is doctor plate, code 6
is an electrode, 7 is a separation plate, 8 is a timing circuit, 9 is a stirring member, T is a toner, and D is
Symbol E indicates a developer, and symbol E indicates a DC voltage power source.

The photoreceptor 1 is formed into a drum shape, and an electrostatic latent image is formed on its peripheral surface. A series of copying processes involves forming an electrostatic latent image on the drum 1 by charging and exposing it to light, developing it, transferring a visible image to a recording sheet, and cleaning the photoreceptor.
This is carried out by rotating the unit in the direction of the arrow and operating its peripheral members in a predetermined order. During this copying process, the developing device is assigned the roles of developing and cleaning the photoreceptor. That is,
When the photoconductor J rotates for the first time, the electrostatic latent image formed on the circumferential surface of the photoconductor 1 is developed, and the photoconductor 1 is rotated for the first time.
During the second rotation, toner remaining on the circumferential surface after the visible image has been transferred is removed from the circumferential surface.

First, development by the developing device will be explained.

The sleeve 3, which is a magnetic brush holder, is made of non-magnetic material and is formed into a hollow cylindrical shape, and is placed in the developer tank 2 so that a part of its circumferential surface approaches the surface of the photoreceptor 1 at a predetermined position. Although it is arranged in the direction of the arrow, it is rotatable around the shaft 31 in the direction of the arrow. A portion adjacent to the sleeve 3 and the photoreceptor 1 is referred to as a developing portion. The direction of the axis 31 is parallel to the rotation axis of the photoreceptor 1. In the inner space of the sleeve 3, a plurality of magnets (not shown), which are elongated rod-shaped and whose magnetic poles are perpendicular to the length direction, are arranged in a predetermined position. , a magnetic field capable of holding the developer D is generated on the right side circumferential surface from the bottom to the top in FIG. Therefore, when the sleeve 3 is rotated in the direction of the arrow by an arbitrary drive mechanism, the developer D, which is a mixture of the magnetic carrier and the toner T, flows from the bottom of the developer tank 2 to the right peripheral surface of the sleeve 3. It will be pumped up.
A doctor plate 5 is arranged near the position where the developer D is pumped up, and regulates the amount of the developer D that is pumped up.

An electrode 6 is arranged connected to the doctor plate 5. The electrode 6 is a long and thin plate with a curvature in its width direction, and the length direction is parallel to the direction of the rotation axis 31 of the sleeve 3, and the curved width direction is approximately concentric with the sleeve 3. However, the distance between the sleeve 3 and the electrode 6 is
The size is determined so that the developer pumped up onto the circumferential surface of the electrode 6 comes into contact with the electrode 6. Electrode 6
At least the surface on the sleeve 3 side is conductive, and a bias voltage can be applied as necessary from the DC voltage power source E, but the switch
Sw is open during development.

Now, the developer D pumped up into the sleeve 3 forms a magnetic brush on the circumferential surface of the sleeve 3 in the developing section, the tip of the magnetic brush contacts the surface of the photoreceptor 1, and the toner T in the magnetic brush forms a magnetic brush on the peripheral surface of the sleeve 3. , photoreceptor 1
It attaches to the electrostatic latent image above and turns it into a visible image. When the developer D that contributed to the development is further transported,
The developer is released from the magnetic field of a magnet (not shown) in the sleeve 3, separated from the circumferential surface of the sleeve 3 by a separation plate 7, and collected into the developer tank 2. In this way, as development is carried out, the toner component in the developer D gradually decreases, so that the toner T stored in the hopper 4 is replenished into the developer tank 2 as appropriate. The supplied toner T is stirred into the developer D by a stirring member 9. Due to this stirring, the toner T rubs against the carrier and is charged by friction to a polarity opposite to that of the electrostatic latent image (negative in this example).

Now, as the copying process progresses and the problematic photoconductor cleaning mode is reached, the timing circuit 8
operates and closes the switch Sw. As a result, a bias voltage having a polarity opposite to that of the toner T in the developer D (positive in this example) is applied to the electrode 6. Then, the toner T in the developer D drawn up onto the circumferential surface of the sleeve 3 is attracted to the electrode 6 and adheres thereto when it comes into contact with the electrode 6. By this,
Some of the toner is removed from the developer D heading toward the developing section, and the toner concentration in the magnetic brush at the developing section is effectively lower than during development. The tip of the magnetic brush with a low toner concentration rubs against the circumferential surface of the photoreceptor 1 on which toner remains in the developing section, and the residual toner is captured by the tip and removed from the circumferential surface. At this time, the toner concentration in the magnetic brush is effectively lowered, so that a sufficient cleaning effect can be obtained in cleaning the photoreceptor. Next, when the state is to be developed again, the timing circuit 8 operates to open the switch Sw, thereby canceling the application of the bias voltage to the electrode 6 and applying the toner T.
The adhesion force of the toner T to the electrode 6 also weakens, and these toner T
is again mixed into the developer material D heading toward the developing section. Therefore, according to this device, the toner concentration in the magnetic brush formed in the developing section is effectively low only during cleaning, and has sufficient density during development, so that a sufficient cleaning effect can be achieved without any deterioration of the developing effect. Obtainable.

In this example, the electrode 6 is electrically insulated from other members during development, but instead of this, the electrode 6 is grounded or changed to a potential suitable for development during development. It's okay,
Furthermore, during development, a bias voltage of opposite polarity to that during cleaning is applied, and during cleaning,
The suction-adhered toner may be actively separated from the electrode 6.

FIG. 2 is a diagram showing another example of a magnetic brush developing device for carrying out the present invention. However, to avoid confusion, the same symbols as in Figure 1 are used for the same equipment.

A feature of the device shown in FIG. 2 is that a roller-shaped doctor member 6 is used to regulate the amount of developer D transported by the sleeve 3 to the developing section.
1 is used, and this roller-shaped doctor member 61 is given a function as an electrode. This eliminates the need to provide a dedicated electrode. During cleaning, as in the above-mentioned example, a bias voltage of opposite polarity to the toner T is applied from the DC voltage power source E to the doctor member 61, and the conveyance amount of the developer D is regulated by the doctor member 61 rotating in the direction of the arrow. At the same time, by attracting and adhering the toner T to the surface thereof, the toner concentration in the developer D heading toward the developing section is reduced. The toner T ₁ adhering to the circumferential surface of the roller-shaped doctor member 61 is removed by the blade 6
2 from the circumferential surface. By doing so, the toner suction and adhesion ability of the circumferential surface is always maintained at its best.

Finally, we will discuss the relationship between the cleaning effect and the magnitude of the bias voltage applied to the electrode, which has a polarity opposite to that of the toner.

FIG. 3 qualitatively shows the relationship between the bias voltage and the cleaning effect. That is, in FIG. 3, the vertical axis represents the amount of toner remaining on the surface of the photoreceptor after the cleaning process, and the horizontal axis represents the absolute value of the bias voltage of opposite polarity to the toner applied to the electrode. Generally, the higher the bias voltage, the higher the cleaning effect. The amount To indicates the degree of cleaning effect achieved by the conventional cleaning method. Whether the amount of residual toner after cleaning changes as shown in graph 3-1, graph 3-2, or graph 3-3 as the bias voltage changes depends on the amount of developer conveyed and the electrode. It depends on the contact area between the developer and the developer. Therefore, in an actual device, a graph as shown in FIG. 3 is qualitatively determined based on the characteristics of the device. Now, if the characteristic curve of the device is as shown in graph 3-1, and the amount of residual toner that can be considered as 0 in practice is T ₁ , then
The value E ₁ determined from FIG. 3 is the minimum value of the bias voltage to be applied to the electrodes of the developing device having characteristics as shown in graph 3-1.

As described above, according to the present invention, when cleaning a photoreceptor using a magnetic brush developing device having a cleaning function, it is possible to obtain a sufficient cleaning effect without impairing the developing effect in any way.
Furthermore, it is possible to provide a photoreceptor cleaning method that can be carried out using a simple device.

In order to improve image quality, the present invention can of course be used in conjunction with a method of applying a bias voltage to the magnetic brush holder, and the amount of developer transported toward the developing section during development and cleaning can be adjusted. It goes without saying that this method can also be used in conjunction with a method of changing the conveyance speed or changing the height of the magnetic brush ears between development and cleaning. . Furthermore, the shapes and configurations of the devices and members shown in FIGS. 1 and 2 do not limit the present invention in any way. For example, it goes without saying that the present invention can be appropriately modified not only to the drum-shaped photoreceptor shown in the above example but also to a belt-shaped photoreceptor.

[Brief explanation of the drawing]

FIG. 1 is a partially cross-sectional side view showing only the essential parts of an example of a magnetic brush developing device for carrying out the present invention, and FIG. 2 is an example of another magnetic brush developing device for carrying out the present invention. FIG. 3, which is a side view showing only the main parts thereof, is a diagram for explaining the influence of bias voltage on the effects of the present invention. 1... Photoreceptor, 2... Developer tank, 3... Sleeve, 6... Electrode, D... Developer, E... DC voltage power supply.

Claims (1)

[Scope of Claims] 1. A developer formed by mixing a magnetic carrier and toner is magnetically held and conveyed to a developing section, where a magnetic brush is formed, and its tip is moved by a photoreceptor. Develop by contacting the surface to be
A photoconductor cleaning method in which a developing device that visualizes a latent image on a photoconductor is used as a cleaning device after the visible image is transferred. A timing circuit applies a bias voltage of opposite polarity to the toner to the electrode to transfer the toner in the developer that contacts the electrode to the electrode only when cleaning the photoreceptor. A method for cleaning a photoconductor, which comprises: lowering the toner concentration of a developer heading toward a photoconductor by suctioning the developer, and cleaning the photoconductor with a magnetic brush having a low toner concentration.