GB1574810A

GB1574810A - Cleaning arrangement for electrostatographic imaging apparatus

Info

Publication number: GB1574810A
Application number: GB5446676A
Authority: GB
Original assignee: Xerox Corp
Current assignee: Xerox Corp
Priority date: 1976-12-31
Filing date: 1976-12-31
Publication date: 1980-09-10

Description

(54) CLEANING ARRANGEMENT FOR ELECTROSTATOGRAPHIC IMAGING APPARATUS (71) We, XEROX CORPORATION of Xerox Square, Rochester, New York, United States of America, a Corporation organized under the laws of the State of New York, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to an electrostatographic imaging apparatus and method, and is particularly concerned with the cleaning arrangement of a liquid-development electrostatographic imaging apparatus.

In a liquid-development electrostatog raphic imaging apparatus, electrostatic latent images are formed on a suitable imaging surface, which is either an insulating surface, or, in an electrophotographic apparatus, is a photoconductor. These electrostatic latent images are then developed by means of a developer liquid.

A typical method of liquid development for electrostatic latent images is that described by R. W. Gundlach in U.S. Patent No. 3084043. In this method, an electrostatic latent image is developed, i.e. made visible, by presenting to the imaging surface a liquid developer on the surface of a developer dispensing member, typically a roller having a plurality of raised portions or 'lands' defining a substantially regular patterned surface and a plurality of depressed portions or 'valleys' below the raised protions. The depressed portions of the developer dispensing member contain liquid developer which is maintained out of contact with the electrostatographic imaging surface. Development is achieved by moving the developer dispensing member loaded with liquid developer in the depressed portions into contact with the imaging surface. The liquid developer is believed to be attracted from the depressed portions of the applicator surface in the charged areas only. The developer liquid may be pigmented or dyed. Practical systems using this method usually employ a reusable, cycling, imaging surface. In these systems a photoconductor such as selenium or a selenium alloy forms the surface of a drum or an endless flexible belt and is charged, exposed to a light and shadow image and developed by bringing the image bearing surface into developing configuration with an applicator containing developing quantities of liquid developer thereon, as just described. The liquid developer is transferred to the imaging surface in image configuration. Thereafter the developer pattern on the imaging surface is transferred to copy paper where the liquid developer may be absorbed by the paper to form a permanent print. During the transfer operation not all of the liquid developer is transferred to the copy paper and a significant quantity may remain on the imaging surface. In order to recycle the imaging surface this developer must be either removed or immobilized, otherwise it will tend to be present as background in subsequent imaging cycles. If the liquid developer is relatively conductive, having a resistivity less than about 1010 ohm-cm, any residue remaining on the imaging surface may lead to degradation of image resolution by lateral conduction.

Procedures to remove the residual developer liquid from the imaging surface after each cycle have been employed.

However, these procedures suffer from the disadvantage that in order to provide the necessary removal of residual liquid developer the cleaning step must be so severe and complete that there may be a progressive degradation of the imaging surface, lessening the useful life span.

It is an object of the present invention to provide an electrostatographic imaging apparatus and method in which this dis advantage is at least partially overcome.

According to the present invention, there is provided an electrostatographic imaging apparatus including a surface capable of supporting an electrostatic latent image and arranged for cyclic movements through a plurality of processing stations, the stations including an imaging station for forming an electrostatic latent image on the surface, a developing station for applying liquid developer to said surface to develop the image, a transfer station for transferring developed images to a transfer surface, a cleaning station for substantially removing residual developer remaining after transfer, and a further station comprising an applicator roller for applying a cleaning liquid to the surface and a device for substantially removing liquid from the surface.

Advantageously the cleaning liquid is of lower electrical conductivity than the liquid developer.

An electrostatographic imaging apparatus and method in accordance with the invention will now be described, by way of example, with reference to the accompanying drawing, which is a diagrammatic crosssectional view of an embodiment of the invention.

Referring to the drawing, an electrostatic latent image is placed on the imaging surface 10 illustrated as a rotating cylindrical drum photoconductor such as a selenium drum by uniformly placing a positive charge on the drum by charging means 11 and then exposing the charged surface to a light-andshadow image through exposure means 12.

The electrostatic latent image is developed at developing station 13 and the developer on the imaging surface in image configuration is transferred to a receiver sheet 14 such as ordinary paper which is moved through the transfer zone in contact with the drum at the same rate and in the same direction as the periphery of the drum. The paper to which the developed image is transferred is held in transfer position by idler 15. The residual developer present on the electrostatographic imaging member is cleaned from the imaging member at a cleaning station.

At the cleaning station, a cleaning blade 16 removes from the imaging surface 10 the residual developer liquid which remains after transfer of the image to the receiver sheet 14. Removed developer liquid is collected by a suitable receptacle 17, and developer liquid is prevented from running back around the drum by means of a blade 18.

As discussed above, despite the cleaning effect of the blade 16, a very thin film of developer liquid remains on the imaging surface 10, and unless it is of very low conductivity it will permit lateral charge conduction, with the resulting image degradation, as the imaging surface 10 moves between the charging means 11 and the exposure means 12. In order to substantially reduce such degradation, the present invention provides a further station 19, which includes an applicator roller 20 and a cleaning blade 21. The applicator roller 20 is arranged to apply a cleaning liquid 22 to the imaging surface 10, and the cleaning blade 21, like the first cleaning blade 16, removes substantially all the liquid from the surface 10. Once again, only a thin film remains.

This time, however, the thin film is mostly of the cleaning liquid, so that by an appropriate choice of cleaning liquid, the conductivity of the film remaining on the surface 10 can be considerably reduced.

Many of the factors which determine the choice of cleaning liquid are the same as those which determine the choice of liquid vehicle for the developer liquid. Thus both liquids are selected so as not to have any adverse physical or chemical effect on either the image surface or any of the machine components which they will contact. Also, of course, both liquids are preferably as nonodorous, nontoxic, and noninflammable as possible. In addition, the cleaning liquid must be miscible with the developer liquid, and must be compatible with its various ingredients, such as dyes, pigments, fixatives or other additives. It is also chosen to have an electrical conductivity lower than that of the developer liquid.

Usually, both liquids are non-aqueous, and may typically be one of, or a mixture of, such liquids as mineral oils, and silicone oils.

Since developer liquid is mixed with cleaning liquid during application of the cleaning liquid at station 19, and since the resulting mixture is cleaned by blade 21, it is clear that an increasing concentration of developer liquid will build up in the cleaning liquid unless steps are taken to prevent this.

It can be arranged, for example, to remove substantially all the liquid collected by the blade 21 so that it does not fall back into the supply of cleaning liquid. In these circumstances, cleaning liquid can be continuously consumed, or can be recycled after suitable treatment to remove the developer liquid from the cleaning liquid. Alternatively, the cleaned-off liquid can be allowed to collect in the cleaning liquid supply, the concentration of developer liquid being kept below an acceptable level by a flow of uncontaminated cleaning liquid, either fresh or recycled.

WHAT WE CLAIM IS: 1. An electrostatographic imaging apparatus including a surface capable of supporting an electrostatic latent image and arranged for cyclic movements through a plurality of processing stations, the stations including an imaging station for forming an

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. advantage is at least partially overcome. According to the present invention, there is provided an electrostatographic imaging apparatus including a surface capable of supporting an electrostatic latent image and arranged for cyclic movements through a plurality of processing stations, the stations including an imaging station for forming an electrostatic latent image on the surface, a developing station for applying liquid developer to said surface to develop the image, a transfer station for transferring developed images to a transfer surface, a cleaning station for substantially removing residual developer remaining after transfer, and a further station comprising an applicator roller for applying a cleaning liquid to the surface and a device for substantially removing liquid from the surface. Advantageously the cleaning liquid is of lower electrical conductivity than the liquid developer. An electrostatographic imaging apparatus and method in accordance with the invention will now be described, by way of example, with reference to the accompanying drawing, which is a diagrammatic crosssectional view of an embodiment of the invention. Referring to the drawing, an electrostatic latent image is placed on the imaging surface 10 illustrated as a rotating cylindrical drum photoconductor such as a selenium drum by uniformly placing a positive charge on the drum by charging means 11 and then exposing the charged surface to a light-andshadow image through exposure means 12. The electrostatic latent image is developed at developing station 13 and the developer on the imaging surface in image configuration is transferred to a receiver sheet 14 such as ordinary paper which is moved through the transfer zone in contact with the drum at the same rate and in the same direction as the periphery of the drum. The paper to which the developed image is transferred is held in transfer position by idler 15. The residual developer present on the electrostatographic imaging member is cleaned from the imaging member at a cleaning station. At the cleaning station, a cleaning blade 16 removes from the imaging surface 10 the residual developer liquid which remains after transfer of the image to the receiver sheet 14. Removed developer liquid is collected by a suitable receptacle 17, and developer liquid is prevented from running back around the drum by means of a blade 18. As discussed above, despite the cleaning effect of the blade 16, a very thin film of developer liquid remains on the imaging surface 10, and unless it is of very low conductivity it will permit lateral charge conduction, with the resulting image degradation, as the imaging surface 10 moves between the charging means 11 and the exposure means 12. In order to substantially reduce such degradation, the present invention provides a further station 19, which includes an applicator roller 20 and a cleaning blade 21. The applicator roller 20 is arranged to apply a cleaning liquid 22 to the imaging surface 10, and the cleaning blade 21, like the first cleaning blade 16, removes substantially all the liquid from the surface 10. Once again, only a thin film remains. This time, however, the thin film is mostly of the cleaning liquid, so that by an appropriate choice of cleaning liquid, the conductivity of the film remaining on the surface 10 can be considerably reduced. Many of the factors which determine the choice of cleaning liquid are the same as those which determine the choice of liquid vehicle for the developer liquid. Thus both liquids are selected so as not to have any adverse physical or chemical effect on either the image surface or any of the machine components which they will contact. Also, of course, both liquids are preferably as nonodorous, nontoxic, and noninflammable as possible. In addition, the cleaning liquid must be miscible with the developer liquid, and must be compatible with its various ingredients, such as dyes, pigments, fixatives or other additives. It is also chosen to have an electrical conductivity lower than that of the developer liquid. Usually, both liquids are non-aqueous, and may typically be one of, or a mixture of, such liquids as mineral oils, and silicone oils. Since developer liquid is mixed with cleaning liquid during application of the cleaning liquid at station 19, and since the resulting mixture is cleaned by blade 21, it is clear that an increasing concentration of developer liquid will build up in the cleaning liquid unless steps are taken to prevent this. It can be arranged, for example, to remove substantially all the liquid collected by the blade 21 so that it does not fall back into the supply of cleaning liquid. In these circumstances, cleaning liquid can be continuously consumed, or can be recycled after suitable treatment to remove the developer liquid from the cleaning liquid. Alternatively, the cleaned-off liquid can be allowed to collect in the cleaning liquid supply, the concentration of developer liquid being kept below an acceptable level by a flow of uncontaminated cleaning liquid, either fresh or recycled. WHAT WE CLAIM IS:

1. An electrostatographic imaging apparatus including a surface capable of supporting an electrostatic latent image and arranged for cyclic movements through a plurality of processing stations, the stations including an imaging station for forming an

electrostatic latent image on the surface, a developing station for applying liquid de veloper to said surface to develop the image, a transfer station for transferring developed images to a transfer surface, a cleaning station for substantially removing residual developer remaining after transfer, and a further station comprising an applica tor roller for applying a cleaning liquid to the surface and a cleaning blade for substan tially removing liquid from the surface.

2. An apparatus according to claim 1 wherein said surface is a photoconductive surface, and the imaging station includes charging means and exposure means for forming electrostatic latent images.

3. An apparatus according to claim 1 wherein said surface is an insulating surface, and the imaging station includes means for depositing on the surface electrostatic charges in image configuration.

4. An apparatus according to any one of claims 1 to 3 including means for maintain ing the concentration of developer in the cleaning liquid below a predetermined con centration.

5. A method of cleaning an imaging surface of an electrostatographic imaging apparatus of the kind in which an electrosta tic latent image is developed on the imaging surface by means of a liquid developer, and the developed image is transferred to a transfer surface; the method comprising substantially removing residual developer remaining after transfer, then applying to the imaging surface by means of an applica tor roller a cleaning liquid of lower electrical conductivity than the liquid developer, and substantially removing liquid from the imag ing surface with a cleaning blade.

6. An electrostatographic imaging apparatus substantially as hereinbefore de scribed with reference to the accompanying drawing.

7. A method of cleaning an imaging surface of an electrostatographic imaging apparatus substantially as hereinbefore de scribed with reference to the accompanying drawing.