Apparatus For Exposing Latent Image Margins In Electrophotographic Copying Apparatus

Abstract

Apparatus for obtaining electrophotographic copies of improved quality and appearance in which a rectangular frame member is disposed adjacent the photoreceptor circumscribing an area on the photoreceptor onto which the images to be reproduced are projected. The frame member includes an internal channel opening downwardly onto the surface of the photoreceptor. Corona discharge means are supported in the channel along the leading side transversely to the direction of movement of the photoreceptor to uniformly charge the surface of the photoreceptor as it is advanced beneath the frame member. Illumination means also are supported internally of the frame member within the channel on all four sides for uniformly discharging the charged surface of the photoreceptor in the areas surrounding the imaged area underlying the frame member to eliminate development thereof.

Description

BACKGROUND OF THE INVENTION

This invention relates generally to electrophotography and more particularly to improvements in electrophotography which result in images which are of a higher quality and more attractive in overall appearance.

In electrophotography or xerography as it is commonly designated, in order to obtain a xerographic copy of an original image, a photoreceptor having a light-sensitive insulating layer supported on a suitable conducting base is uniformly charged by charging means such as a corona discharge device and the charged area of the photoreceptor is then exposed to a light pattern which corresponds to the original image. The result is to form a corresponding charge pattern on the photoreceptor commonly referred to as a latent electrostatic image. The latent electrostatic image is then developed by contacting the photoreceptor with charged pigmented particles referred to as toner particles which are selectively attached to latent image areas to form a corresponding visible image. In the usual manner of carrying out the xerographic process during the step of uniformly charging the light-sensitive insulating layer, a large area sufficiently covering the effective area to be exposed to the light image will be charged. Therefore, after exposure, the marginal areas surrounding the exposed area remain unexposed and hence still carry a charge. When the photoreceptor is then subjected to development, toner is attracted to the marginal areas in addition to the image area. This is due to the fact that toner particles which are charged to a polarity opposite to that of the charge forming the latent electrostatic image are attracted to the photoreceptor according to the density of the residual charge. Since the residual charge density of the marginal areas is highest, these areas are developed most highly. This results in surrounding the developed image with a black frame, which is unpleasant to the eye. Also, when such occurs excessive quantities of toner will be consumed in the process so that the toner concentration in the developer material is reduced at an unnecessarily rapid rate. This therefore causes a degradation of the image quality over a short period of running time and requires continual operator attention.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to improve the quality and appearance of electrophotographic images.

It is another object of the present invention to provide an improved electrophotographic arrangement which produces copies having increased quality and appearance.

It is yet a further object of the present invention to provide an improved electrophotographic arrangement which eliminates development of the margin areas surrounding the image area.

These and other objects of the invention are attained in an electrophotographic arrangement in which a frame member is disposed adjacent the photoreceptor circumscribing the area on the photoreceptor onto which the images to be reproduced are projected. The frame member includes an internal channel opening downwardly onto the surface of the photoreceptor. Corona discharge means are supported transversely to the direction of movement of the photoreceptor internally of the frame member along one side thereof within the channel to uniformly charge the surface of the photoreceptor as it is advanced beneath the frame member. Illumination means are supported internally of the frame member within the channel for uniformly discharging the charged surface of the photoreceptor in the areas surrounding the imaged area underlying the frame member to eliminate fringe fields surrounding the image area and hence eliminate development thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross sectional illustration of an electrophotographic apparatus as contemplated by the present invention.

FIG. 2 is an enlarged schematic cross sectional illustration of a portion of the frame member of FIG. 1.

DESCRIPTION OF A PREFERRED EMBODIMENT

Referring now to FIG. 1, a xerographic sheet or plate 2 which comprises a light-sensitive insulating layer supported on a conducting backing layer is supported on a support 1 and may be advanced in the direction of the arrow. The xerographic sheet or plate 2 is held in position by an exposure frame 3 disposed thereabove.

The xerographic sheet or plate employed in the present invention may comprise any photoconductive member suitable for use in electrophotography. Suitable photoconductive members include for example, photoreceptors prepared by laying vacuum evaporated coatings of selenium on electroconductive supports, photoreceptors formed by coating on electroconductive support members layers of film-forming insulating resins having dispersed therein pulverized photoconductive materials such as cadmium sulfide, zinc oxide or titanium dioxide, and photoreceptors formed by coating organic photoconductive films on electroconductive supports. Such photoreceptors may also contain various sorts of additives either singly or in combination so as to increase photosensitivity or to give optimum spectral sensitivity and such photoreceptors are contemplated within the scope of the present invention.

As will be appreciated, it is convenient to selectively use various photoreceptive members according to the object or purpose of use as is well known. For instance, in the case of selenium vacuum evaporated films, it is preferable to transfer the images to other image receiving members, while in the case of organic photoconductors, it may be preferred to use the photoreceptor for the purpose of obtaining transparent images by making use of its optical transparency. On the other hand, in the case of resin layers dispersed with zinc oxide, titanium dioxide or the like, when applied on suitable supports, such as paper, there may be no need of transferring the images which may be directly fixed and preserved as a record. This may also be true in the case where an organic photoconductor is laid on a paper sheet. It will also be appreciated that in case of using a combination of photoconductive powder-resin layers dispersed with the above-mentioned or equivalent materials, or organic photoconductors, it is also possible to form an image on other recording media by transfer.

According to the invention, the exposure frame 3 is generally of a rectangular configuration similar in nature to a picture frame with four side frames which are open downwardly and include therein a suitable discharging light source 6. One of the four frames, namely the one 4' on the side of insertion of the sheet 2, is provided with a corona discharge electrode means 7. Reference numeral 8 designates a projection lens system and reference numeral 9 designates a light transmitting original. Reference numeral 10 designates a light source for illuminating original image 9 for projection onto the surface of photoreceptor 2.

In operation, as the sheet 2 is fed in the direction of the arrow, it is charged by the corona discharge in the channel 5 of frame 4', and advancement of the sheet is stopped so that the charged area is held within the exposure frame 3.

In this position, the projecting light source 10 or a shutter means (not shown) is then actuated to expose the charged area of the sheet 2 to a light image corresponding to the light transmitting original 9 focused through the projecting lens system 8. As a result, the charge on the sheet 2 is discharged according to the pattern of the projected light image to form a corresponding latent electrostatic image.

Simultaneously with the exposure or prior to the resumption of the feeding of the sheet 2, the discharging light source 6 is energized. As a result, the charge on the area of the sheet 2 beneath the frame 3 is discharged. Then, the sheet 2 is fed by a length corresponding to another pitch, that is, a length corresponding to the distance between the frames 4' and 4. At this time, the subsequent area of the sheet 2 is charged by the corona discharge.

Although the area of the sheet 2 facing the frame 4' when the sheet 2 is held stationary may be irregularly charged, if corona discharge means 7 is continually energized, this has no undesired effect since the irregularly charged area will be subsequently discharged by the discharging light source 6.

The exposure frame 3 may be disposed in close contact with the sheet 2, or it may be spaced from the sheet 2 by a slight distance, of the order of about 1 mm. To the end of preventing any leaking discharge through the lower end of the frame 3 it may be desirable to have both lower ends 11 and 12 or perhaps one lower end 11 of the frame 4 pointed.

The exposure frame 3 as previously pointed out is generally of a rectangular configuration similar in nature to a picture frame with a discharging light source 6 provided along each side thereof within the channel. The corona discharge electrode means however is provided only at the side thereof at which insertion of the sheet 2 occurs. However, as an alternative embodiment, the discharging light source 6 and the corona discharge electrode means 7 may be provided in the frame only on the side of insertion of the sheet 2.

The corona discharge electrode means 7 consists of a metal wire having a diameter of about 10 to 50 microns, on which is impressed a high voltage to cause the corona discharge. In the preferred arrangement it is desirable to energize the corona discharge only while the sheet 2 is being advanced. To this end, the corona discharge electrode means 7 may be energized and de-energized in conjunction with energization and de-energization of the projection light source 10 which is energized only when the sheet 2 is stopped. The discharging light source 6 however, may be energized either during the exposure or subsequent thereto to eliminate any residual charge on the area of the sheet beneath the frame 4'. However, it is preferred to energize light source 6 simultaneously with energization of projection light source 10. The discharging light source 6 may use means to provide a number of discharging light beams, a long light source such as a fluorescent lamp or a light transmitting means using optical fiber, for the purpose of achieving uniform discharging of the area of the sheet 2 beneath the frame.

Thus, as has been described in the foregoing, according to the present invention, a discharging light source is provided in an exposure frame for discharging the marginal area of a xerographic plate or sheet beneath the frame so as to prevent the attachment of toner to the marginal areas. The invention additionally contemplates minimizing the size of the corona discharge electrode means thus effecting extremely efficient charging and exposure. This arrangement therefore results in copies having increased quality and appearance.

While the invention has been described with reference to preferred arrangements and embodiments, it will be generally understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the true spirit and scope of the invention.

Claims

What is claimed is:

1. In an electrophotographic reproducing apparatus in which a photoreceptor is advanced in a stepped intermittent manner, apparatus for charging and exposing said photoreceptor including,

a light source for illuminating an image to be reproduced,

means for projecting said illuminated image onto the surface of said photoreceptor,

a frame member disposed adjacent said photoreceptor and circumscribing the area on said photoreceptor onto which said illuminated images are projected, said frame member including an internal channel opening downwardly onto the surface of said photoreceptor,

corona discharge means supported transversely to the direction of movement of said photoreceptor internally of said frame member along one side thereof within said channel,

means for energizing said corona discharge means when said photoreceptor is being advanced to uniformly charge the surface of said photoreceptor as it is advanced beneath said frame member, and

illumination means supported internally of said frame member within said channel for uniformly discharging the charged surface of said photoreceptor in an area surrounding the imaged area underlying said frame member to eliminate the unwanted fringe fields surrounding the imaged area.

2. Apparatus according to claim 1 wherein said illumination means is energized simultaneously with the energization of said light source.

3. Apparatus according to claim 1 further including means for de-energizing said corona discharge means upon interruption of the advancement of said photoreceptor.

4. Apparatus according to claim 1 further including means for connecting said corona discharge energizing means to said corona discharge means when said photoreceptor is being advanced and to said light source and said illumination means when advancement of said photoreceptor is interrupted.

5. In an electrophotographic reproducing apparatus in which a photoreceptor is advanced in a stepped intermittent manner, apparatus for charging and exposing said photoreceptor including,

a light source adapted to illuminate an image to be reproduced,

means for projecting illuminated images onto the surface of said photoreceptor,

a frame member positioned adjacent said photoreceptor enclosing an area on said photoreceptor within which illuminated images are projected, said frame member having an internal channel opening downwardly onto the surface of said photoreceptor,

corona discharge means supported transversely to the direction of movement of said photoreceptor internally of said frame member along one side thereof within said channel,

means for energizing said corona discharge means when said photoreceptor is being advanced to uniformly charge the surface of said photoreceptor as it is advanced beneath said frame,

illumination means supported internally of said frame member within said channel adapted when energized to uniformly discharge the charged surface of said photoreceptor in the area underlying said frame member,

means for energizing said light source to project an image to be reproduced onto the photoreceptor in the area within said frame member, and

means for energizing said illumination means to discharge the charged surface of said photoreceptor underlying said frame member to eliminate unwanted fringe fields surrounding the imaged area.

6. Apparatus according to claim 5 wherein said illumination means is energized simultaneously with the energization of said light source.

7. Apparatus according to claim 5 further including means for de-energizing said corona discharge means upon interruption of the advancement of said photoreceptor.

8. Apparatus according to claim 5 further including means for connecting said corona discharge energizing means to said corona discharge means when said photoreceptor is being advanced and to said light source and said illumination means when advancement of said photoreceptor is interrupted.