JPS5815790B2 - Electrostatographic developing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a toner latent image development apparatus and, more particularly, to a development apparatus that uses a toner-loaded donor member to apply toner particles to the surface of an electrostatic latent image.

In general, xerographic copying processes involve first forming a latent image on a specific surface and then developing it into a visible image with a powder commonly called toner. It must be brought close to the surface to adhere to the image contour according to the latent image pattern, and a donor member is commonly used for this purpose.

This donor member may be in the form of a roll, an endless belt, or the like, but in any case, it first comes close to the surface of the latent image on which toner particles are to be deposited and developed.

The toner particles then detach from their donor and adhere to the latent image surface to form a visible image thereon.

Various proposals have been made to improve the operation of the donor member in this system. This eliminates the risk of toner from the donor member adhering to non-imaging areas.

That is, the toner on the donor member does not come into contact with the latent image surface and therefore does not adhere to the non-imaged areas.

This is described in US Pat. No. 3,232,190 as a technique for keeping a layer of toner particles firmly spaced from the surface of the latent image to be developed.

In this case, an electrostatic force stronger than the toner particle holding force on the donor member is generated against the high voltage image pattern charging area, and the toner is attracted and adhered to the image area.

However, although there is electrostatic force in other areas on the latent image surface, that is, non-image forming areas, this electrostatic force is smaller than the electrostatic force of the donor member that holds the toner particles.
As a result, no toner will adhere to the non-image forming areas.

The density of toner particles deposited on the final copy also depends on the size of the gap between the donor member and the latent image surface.

That is, since the electrostatic field on the surface of the latent image decreases as the gap becomes larger, it is necessary to strictly control this gap peeling.

It has been found that relatively loose gaps do not result in complete development.

The development effect can also be enhanced by applying an electric potential to the donor member itself that helps the toner particles try to overcome the forces pulling them against the donor member; The toner moves randomly to the latent image surface and also adheres to non-imaged areas.

This phenomenon is known as background development and leads to poor copy quality.

Another known technique for separating toner particles from the donor member is U.S. Pat. No. 3,257,223, which results in a cloud of toner particles between the donor member and the latent image surface.

To load toner particles onto the donor member, a voltage of opposite polarity to the toner particles is applied to its conductive base to attract the toner particles to the base surface between the grid elements.

Then, when development is to be carried out, the voltage on the conductive base is cut or a voltage of the same polarity as the toner particles is applied to separate the toner particles from the donor member and bring them into contact with the surface of the latent image in the form of a cloud. .

The upper conductive grid serves to cut the electric field lines from the conductive base of the donor during its toner deposition and release, creating particularly strong fringe-like electric fields that exist on the surface at various potential differences.

Since the toner is in the form of a cloud, the toner will also adhere to non-imaging areas.

Yet another donor member is of the fringe-like electric field formation type.
It is described in US Pat. No. 3,203,394.

In this case, the donor element consists of a conductive base with a weakly insulating layer on top and a highly insulating post pattern as a top layer on top of which the donor is introduced into the development zone. The shape is such that toner can be easily attached to the peripheral surface of the toner prior to use.

In operation, the donor member is first electrostatically charged and then introduced into a toner deposition station.

Between the charging station and the toner deposition station, the weak insulating layer loses its charge, thus creating a fringe-like electric field on the surface between the insulating post and the weak insulating interlayer.

As a result of this fringe-shaped electric field, toner particles are located only between the highly insulative posts, resulting in discontinuous deposition of toner on the donor member.

This is never desirable.

The reason for this is that there is a limit to the amount of toner that can enter the development area.

Furthermore, the superposition of the toner particles on the donor onto the imaging areas on the latent image surface does not necessarily coincide synchronously.

If the toner particles and the surface of the latent image do not match in this way, there will be gaps in the latent image area and complete development will not be possible.

The present invention creates an electric field between the toner layer and the donor member in the development area, so that the toner can be used for developing the surface of the latent image to be developed, and does not adhere to the non-image forming area. The purpose is to provide a developing device.

In one embodiment, the donor member is a rotatable endless belt that is passed near the toner deposition area and then the latent image surface.

When an electric field is applied to the toner on the belt-like donor member, the electric field activates toner particles on the donor that pass through the development zone.

Further, among the activated toner particles, the toner that is not attached to the latent image area returns to the surface of the donor member from which the toner left in the development area and is attached thereto.

In the development area, the toner is separated from the donor member by the action of the electric field, while the layer remains under the action of the electric field.

With such a construction, toner particles do not stick to the non-imaging areas and therefore no toner sticks to the background of the copy.

Further, with this structure, the development quality does not deteriorate even if the gap distance between the donor member and the development surface is not strictly controlled.

Accordingly, one object of the present invention is to provide an improved development apparatus for electrostatic latent images.

Another object of the present invention is to provide an improved developing device capable of applying toner to a latent image surface without directly contacting the donor member to which the toner is attached. .

Yet another object of the present invention is to provide an improved development device that allows for control of toner particles in the development zone.

Another object of the present invention is to provide a development system that does not allow background development.

The present invention comprises an apparatus for developing an electrostatic latent image comprising bringing a donor member loaded with toner close to a latent image surface and transferring the toner to the latent image surface in a contour corresponding to the latent image pattern. This is the summary.

When the donor member carrying the toner is passed through the development area, the toner particles subjected to the action of the electric field in the development area are made to be in a state where they tend to adhere to the surface of the latent image.

In addition, this electric field causes the toner to be activated in this way.
Toner that does not adhere to the latent image surface is re-adhered to the donor member after exiting the development area.

According to one embodiment of the invention, the layer of toner on the donor member is separated from the surface by the gap distance between it and the latent image surface, and the electric field causes the toner to adhere to or conversely separate from the donor member. The reduction is sufficient.

In yet another embodiment, the toner layer may be in contact with the latent image surface, and the action of the electric field controls toner action in the development areas so that toner particles do not adhere to non-imaged areas. That's true.

Other objects and features of the invention will become apparent from the following description of the embodiments.

The present invention can be used with any type of copying machine that uses toner to develop a latent image.

Therefore, in order to understand the present invention, the xerographic copying machine will be explained below.

The continuous motion xerographic copying machine shown in FIG. 1 has a photosensitive member in the form of a drum 11 for forming an electrostatic latent image to be reproduced, and the drum 11 is powered by a shaft-like donor from a suitable power source. Rotational drive through one member 12 causes its surface to pass sequentially through copy processing stations A-E.

A layer of electrically conductive material is applied to the circumferential surface of the drum, and a photoconductive layer such as amorphous selenium is applied thereon.

Copying operations are performed while the drum passes through five copy processing stations located around the drum.

The five copy processing stations are charging station A, exposure station BJ, image station C, transfer station D1, and cleaning station E.

As this drum surface passes through charging station A and exposure station B, an electrostatic latent image is formed thereon.

Charging station A is equipped with a corona discharge device that uniformly charges the photoconductive layer.

Exposure station B also includes a device for projecting a light beam pattern of the image to be reproduced onto the surface of the drum, the light image projected onto the charged photoconductive layer of the drum being synchronized with the movement of the drum. , thereby selectively dissipating the charge on the drum to form an electrostatic latent image thereon.

After the electrostatic latent image is formed after passing through the two stations A and B, the latent image enters the developing station C, where a developer (hereinafter referred to as toner) consisting of electrostatic powder made of colored resin, for example, is applied. ) is deposited on the drum according to the image contour.

Details of this developing station will be described later.

After development, the powder image formed on the drum enters transfer station D, where the toner image is transferred from the drum surface to an image support material such as paper, a continuous web, or the like.

Transfer of the toner image onto the copy sheet is accomplished, for example, by electrostatic attraction of the toner image from a drum onto the sheet by a corona discharge device.

The copy sheet with the toner image transferred thereto is then passed through a fusing station where it is fused into a permanent image.

This fixing device may be any known fixing device.

The final processing station is cleaning station E.
The cleaning station E includes a cleaning device, such as a brush, in contact with the photoconductive surface of the drum.

This cleaning station E is for stripping residual toner remaining on the photoconductive surface after transfer from the drum surface before the start of the next copying cycle.

The developing device according to the present invention is located in the above-mentioned developing station C, and as is clear from FIG. It's coming.

In the embodiment shown, the donor member is in the form of an endless belt and rotates in a clockwise direction.

The toner particles adhering to this belt pass around a roller 13 and an electric field generating device 3 where they are transferred onto a drum, forming a toner image thereon.

As the belt transports the toner toward the development area, a corona discharge device 16 imparts an electrostatic charge to the toner so that all toner particles are charged to the same charge.

In FIG. 2, which shows details of the donor member, the belt-like donor member 12 is insulative and made of a triboelectric material capable of adhering toner thereto by friction with the toner.

However, it is not always necessary to place the toner on the belt 12 due to the frictional charging relationship with the toner.

In any case, this deposition of toner particles is conveniently effected by vibrating the toner reservoir 17 and grounding the roller 13 by suitable means.

Various methods can be considered for attaching this toner to the donor member.

For example, the donor member can be made of a material suitable for having a triboelectric relationship with the toner particles, and the toner can be cascaded onto the surface of the donor member along with the carrier beads.

Another known method for depositing toner particles on the surface of the donor member is to apply a cloud of charged toner to the donor member.

After depositing the toner particles on the belt and introducing it into the development station, the layer of toner particles is uniformly charged by a corona discharge device 16.

This creates a good electrostatic adhesion relationship between the toner and the imaging area of the drum during development.

The charge on the toner layer at this time is determined by the developing method employed.

For example, it is common to charge the xerographic plate to a high voltage of positive polarity and then expose the non-imaged areas to lower the potential on this portion of the drum.

In this case, when a high potential area is to be developed, the toner is negatively charged.

However, when a low potential area is to be developed, the toner is positively charged.

The electric field generator 3 includes a grounding plate 15 and a bias plate 14, the grounding plate 15 being behind the belt 12 and forming a surface on which the belt 12 rests.

This ground plate 15 extends from the development area through the charging area as shown, and the other part of the electric field generator 3 is a bias plate 14 which provides the surface on which the belt rests after leaving the development area. .

These two grays N4, 15 are not in electrical contact with each other.

This is because these two members are combined to generate an electric field in the development area as shown in FIG. 3.4.

In FIG. 1, there is an insulating gap between plates N4, 15, while as shown in FIG.
1 may be provided between these two plates.

The charge on bias plate 14 is proportional to the charge on the toner particles and is of opposite polarity.

As shown in FIG. 2, when the toner is negatively charged by the corona discharge device 16, the bias potential on the plate 14 becomes positive.

On the other hand, when the toner is positively charged, bias plate 1
4 should be biased to negative polarity.

Bias plate 14 and ground plate 15 create an electric field between the plates that pulls toner in the development area toward bias plate 14.

Figures 3 and 4 show details of the development area, where plate 15 is grounded and the other plate 14 is positively charged, so that a fringe-like electric field effect is generated between the plates near the development area. occurs in

This electric field extends through the donor member 12 and the toner layer 19, the electric field lines being shown by the dashed lines passing between the plates 14,15.

The purpose of this electric field is to activate the toner particles while they are in the development zone, making them susceptible to adhesion to the electrostatic latent image on the drum.

The term "activation" refers to reducing the adhesion of toner particles to the donor member, making it easier for the toner to separate from the donor member.

In non-contact systems where a gap separates the toner layer from the drum as shown in FIGS. 3 and 4, the electric field is the force that actually separates the toner from the donor member in the development area.

Also, for example, in a system where a single layer of toner is brought into contact with the drum, the attraction of the toner to the donor member is simply reduced to zero, such that the latent image area on the drum attracts the toner thereto.

In the above-described non-contact systems, it is preferred to keep the toner particles sufficiently separate from the donor member so that they can easily adhere to the surface to be developed.

However, it is equally important to have sufficient control of the active toner particles to prevent toner from adhering to the non-imaging areas of the drum.

In FIG. 3, the (-F) symbol indicates the imaging area of the drum, and the rest of the drum is the non-imaging area.

The toner particles activated by the electric field generated by the plates 14 and 15 do not adhere to the image forming area.

However, at this point in the illustration, the imaging area is not near the donor member, so no activated toner is in the gap with the latent image surface.

Instead, the toner particles that have completed their movement due to the electric field generated by the plates 14 and 15 are adsorbed onto the donor member again by the electric field generated by the grate 14.

FIG. 4 shows a state in which the imaging area is in the development area and is capable of receiving toner from the donor member, in which case the activated toner is removed by the electric field from the imaging area of the drum. A powder image will be created by suction through the gap onto the drum surface.

In this development area, toner particles that have not adhered to the drum are again adhered to the plate member 15 in response to the electric field of the donor member.

As can be seen from the foregoing, even if all the toner on the developer member is activated, there is a need to completely control the movement of this toner at any time.

This toner control is achieved by using a development system in which an electric field that liberates toner particles from the donor moves the toner through the gap to the surface of the latent image. It acts like this.

Additionally, all toner is activated during the passage of the donor member through the electric field generating device.

This allows a non-contact system to completely transfer the toner to the drum and completely develop the latent image.

In addition to preventing toner from adhering to the background area, the present invention also allows relatively free setting of the gap between the donor member and the latent image surface.

One of the problems with previously known devices is that when the gap between the latent image surface and the donor member is large, an electric field strong enough to reliably move the toner particles away from the donor member can be applied to the imaging area of the drum. It was not necessarily impossible to obtain from

The present invention provides a developing device in which the above-mentioned gap may be considerably large.

This is due to the electric field that activates the toner. If the toner particles remain attached to the donor member during development, the electric field from the drum will move the toner particles through the gap and release the toner from the donor member. It will be lower than you need to pull it up.

FIG. 5 shows another embodiment in which an endless insulating belt 20 is driven counterclockwise around rollers 21 and 22. FIG.

Toner is deposited from the vibration reservoir 17 onto the outer peripheral surface of this belt.

To aid in the adhesion of toner particles to the outer circumferential surface of belt 20, a ground electrode 23 located above the hopper or toner reservoir 17 extends toward the development area.

The toner particles attached to the belt 20 are introduced into the development area of the drum 11 as they move.

Behind the donor belt 20 in this development area is a second
It has the same structure as shown in the figure.

In addition, the grounding plate 3 is made of an insulating material 24 with a plate 25.
insulated from

Note that the polarity of the plate 25 is opposite to that of the toner.

As is clear from FIG. 6, the electric field generated in the development area between plates 23-25 is the same as that described in FIGS. 3-4.

As the imaging region shown in FIG. 6 passes through the development region, toner particles activated by the electric field between plates 23,25 are
It is freely drawn to its imaging area on drum 11.

Also, the toner that is not drawn up by this drum 11 leaves the development area and is drawn back onto the belt.

Therefore, no floating toner remains in the development area.

Development systems other than those described above are of course possible; for example, the charge charged by the donor member to the toner thereon can be made positive or negative depending on the charging state of the latent image; The shape of the member does not necessarily have to be an endless belt, but may be a roll or a continuous web.

Also, in the case of an endless belt donor, it is necessary to remove residual toner from the belt in order to avoid image retention, and this can be done using a suitable cleaning device such as the brush 4 shown in FIG. done by.

The developing device described here is used in a large xerographic copying machine that develops electrostatic latent images, but it can of course be applied to electrostatic photography and electrophotographic techniques other than this xerographic type. .

Although the present invention has been described above with reference to a specific embodiment thereof, the present invention is of course not limited to this embodiment, but includes various design changes.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a developing device according to the present invention for a xerographic copying machine, FIG. 2 is a detailed diagram of one embodiment thereof, and FIG.
, 4 are explanatory diagrams of the electric field in the developing area, FIG. 5 is a detailed diagram of another embodiment, and FIG. 6 is a detailed diagram of another state of the electric field. C-Development zone, 3-Electric field generator, 11-Xerographic drum, 12-Donor for depositing toner, 19-Toner particles.

Claims (1)

[Scope of Claims] 1. A device for developing a surface supporting an electrostatic latent image with charged toner in a developing region, the device being adapted to transport charged toner from its supply source to the developing region,
a donor member that supports the toner so that it does not come into contact with the surface in the development area; and a donor member that supports the toner so that it does not contact the surface; two electrodes spaced apart with a gap between them, and an electric field between the gap having a polarity and magnitude such that toner on the donor member moves away from the member and toward the surface; A developing device comprising: means for applying a bias voltage generated on a donor member.