WO1989012260A1

WO1989012260A1 - Cleaning station

Info

Publication number: WO1989012260A1
Application number: PCT/NL1989/000041
Authority: WO
Inventors: Benzion Landa
Original assignee: Spectrum Sciences BV
Current assignee: Spectrum Sciences BV
Priority date: 1988-06-06
Filing date: 1989-06-05
Publication date: 1989-12-14
Anticipated expiration: 1990-12-06

Abstract

A cleaning system for a liquid toner electrophotographic system having a photoconductor surface, the cleaning system including apparatus for wetting the photoconductor surface with a cleaning liquid comprising an essentially unpigmented carrier liquid containing a lubricant.

Description

CLEANING STATION

FIELD OF THE INVENTION The present invention is related to liquid toner electrophotography generally. BACKGROUND OF THE INVENTION

In electrophotography it is normally necessary to remove residual toner from the photoconductor surface following transfer of the image to a substrate. A cleaning system operative to remove residual toner by flushing the photoconductor surface with a cleaning liquid is described in U.S. Patent 4,439,035 to the present inventor.

In single color systems, as for example in U. S. Patent 4,436,054; liquid toner, comprising pigmented toner particles, carrier liquid and additives is used to wet a cleaning roller to aid in removal of the residual toner. It is feasible to use liquid toner instead of clear liquid since the liquid toner comprises only about 1.5% pigmented material.

In multi-color electrophotography employing a single photoconductor, it is necessary to clean the photoconductor between the application of different colors and to avoid contamination between colors. Accordingly a speedy and efficient photoconductor cleaning system is required to permit efficient multi-color electrophotography. In some multi-color systems a black pigmented liquid toner is used for cleaning for all of the colors, and the material removed is returned to the black pigmented liquid toner reservoir.

Alternatively, as in U. S. Patent 4,627,705, different toners are used for cleaning after printing with different colors. SUMMARY OF THE INVENTION The present invention seeks to provide highly efficient photoconductor cleaning for liquid toner electrophotography. There is thus provided in accordance with a preferred embodiment of the invention a cleaning system for a multi¬ color liquid toner electrophotographic system including a photoconductor surface, the cleaning system comprising apparatus for wetting the photoconductor surface with a cleaning fluid comprising an essentially unpigmented carrier liquid to which is added a lubricant.

The phrase "essentially unpigmented carrier liquid" is used throughout to denote either a clear carrier liquid or a liquid toner which retains only about 1% or less of the normal pigmented particles normally found in a liquid toner. In accordance with a preferred embodiment of the invention there is also provided an apparatus for filtering the cleaning fluid downstream of the photoconductor surface to remove most undissolved material from the cleaning liquid. Further in accordance with a preferred embodiment of the invention the lubricant is selected from the following: lecithin, Basic Barium Petronate, a silicone material or any other suitable lubricant.

In a preferred embodiment of the invention the apparatus for filtering retains up to 0.1% of solid toner materials in the cleaning fluid.

BRIEF DESCRIPTION OF THE DRAWING The present invention will be understood and appreciated more fully from the fol lowing detailed description taken together with the drawing in which:

Fig . 1 is a generalized il lustration of electrophotography apparatus constructed and operative in accordance with a preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION Reference is now made to Fig. 1 which illustrates electrophotographic imaging apparatus constructed in accordance with a preferred embodiment of the present invention. This and other embodiments of the invention are described for the case of liquid toners with negatively charged particles, and positively charged photoconductors. For positively charged toner, the polarities of the voltages given would be reversed. In a preferred embodiment of the invention the toner of Example 1 of U. S. Patent 4,794,651 can be used, but a variety of liquid toner types are useful in the practice of the invention.

The apparatus of Fig. 1 will be described in the context of a monochromatic system, it being appreciated that the present invention is applicable and particularly useful in a multi-color system, where for example the liquid toner in the developer is changed between he application of different colors, or where separate developers are provided for each color.

As in conventional electrophoretic imaging systems, the apparatus of Fig. 1 comprises drum 10 arranged for rotation about an axle 12 in a direction generally indicated by arrow

14. The drum 10 is formed with a cylindrical photoconductive surface 16.

A corona discharge device 18 is operative to generally uniformly charge the photoconductive surface 16 with a positive charge. Continued rotation of the drum brings the charged photoconductor surface 16 into image receiving relationship with an exposure unit including a lens 20, which focuses a desired image onto the photoconductor surface 16, selectively discharging the photoconductor surface, thus producing an electrostatic latent image thereon. Continued rotation of the drum 10 brings the charged photoconductor surface 16 bearing the electrostatic latent image into a development unit 22 which is operative to apply a liquid toner to develop the electrostatic latent image. For multi-color copying the development unit 22 can for example comprise a plurality of developers, one for each color, which are selectively engaged as in U. S. Patent 4,690,539; which is incorporated herein by reference, or a single development station where the liquid toner is changed between colors, or any other suitable development system.

The term multi-color as used herein includes both full color processes and systems in which a single color, which can be changed, is printed at one time.

In accordance with a preferred embodiment of the invention, following development of the latent image, the photoconductor surface 16 passes a metering roller 26, preferably of the type illustrated in Fig. 1 of U. S. Patent

4,411,976; which is incorporated herein by reference.

Downstream of metering roller 26 there is provided apparatus 40 for transfer of the developed image from the photoconductor surface 16 to a substrate 130, such as paper. The direct transfer is effected by the provision of guide rollers 132, 134 and 136, which guide a continuous web of substrate 130, and a drive roller 138, which cooperates with a support web 140. A suitable charging device, such as a corona discharge device 142, charges the substrate at a transfer location, for effecting electrophoretic transfer of the image from the photoconductor surface 16 to the substrate 130.

Following the transfer of the toner image to the substrate 130, the photoconductive surface 16 engages a cleaning station 49. This station may be any conventional cleaning station or preferably the cleaning station shown in Fig. 1, comprising a cleaning roller 56 which may comprise a suitable resilient material such as an open-cell polyethylene foam or preferably a resilient material such as polyethylene or neoprene having externally open or exposed, internally closed or isolated surface cells. The cleaning station 49 also comprises a squeegee roller 50, having a non-cellular polyurethane body formed around a shaft with a dielectric insulating layer therebetween, if desired.

Squeegee roller 50 is driven so that its surface moves opposite to that of surface 16 at their nip to provide scrubbing action for removal of residual particles and carrier liquid not transferred to the substrate 130.

Cleaning roller 56 and squeegee roller 50 are urged against the drum surface 16 by any suitable means (not shown) . Squeegee roller 50 is rotated in the direction indicated by an arrow 57 at a rate such that its surface velocity at the nip with the surface 16 is preferably equal to the velocity of that surface.

A conduit 54 supplies cleaning liquid to the nip of the squeegee roller 50 and the cleaning roller 56 for the removal of residual toner particles

Cleaning systems of the type described hereinabove are disclosed in U. S. Patent 4,439,035; which is incorporated herein by reference. Alternatively cleaning apparatus such as described in U.S. Patent 4,392,742, or any wetted cleaning roller as is known in the art can be employed.

In a preferred embodiment of the invention the cleaning liquid comprises essentially unpigmented carrier liquid which may be derived from liquid toner by removal of most of the pigmented particles, and which retains lubricants therein.

In an alternative preferred embodiment, the cleaning liquid comprises a carrier liquid such as Isopar to which lubricants such as small quantities of lecithin or Basic Barium Petronate or other suitable charge director, or a silicone material, or other suitable lubricant have been added.

A small portion of the toner particles (up to about 10% of the concentration in the toner or 0.1% non volatile solids in the toner) may remain in the cleaning fluid, and that these particles may also act as a lubricant. It has been found that Isopar, commonly used as the carrier liquid for liquid toners, may have an abrasive effect on the photoconductive drum, in the absence of lubricant. The cleaning fluid which drains from the photoconductive surface 16 is typically collected in a collection container 60. The liquid is then typically pumped by a pump 62 via a filter 64 which removes most but normally not all of the pigmented particles from cleaning fluid. Typically a 0.1% concentration of toner material remains in the cleaning fluid.

From the filter 64, the filtered cleaning fluid typically is supplied to a storage tank 66, from which it is pumped by a pump 68 through conduit 54, in a recycled manner.

Any residual charge left on the photoconductive surface 16 is removed by flooding the photoconductor surface with light from a lamp 58.

It will be appreciated by persons skilled in the art that the present invention is not limited by what has been particularly shown and described hereinabove. Rather the scope of the present invention is defined only by the claims which follow:

Claims

1. A cleaning system for a liquid toner electrophotographic system including a photoconductor surface, the cleaning system comprising: means for wetting the photoconductor surface with a cleaning liquid comprising an essentially unpigmented carrier liquid containing a lubricant.

2. A cleaning system according to claim 1 and also comprising: means for filtering the cleaning liquid downstream of the photoconductor surface to remove most of the solid material from the cleaning liquid.

3. A cleaning system according either of claim 1 or claim 2 and wherein said lubricant is selected from the following: lecithin, Basic Barium Petronate, a charge director or a silicone material.

4. A cleaning system according to claim 2 wherein said means for filtering retains up to 0.1% of pigmented toner materials in the cleaning liquid.

5. A cleaning system according to claim 1 wherein said lubricant comprises up to 0.1% of solid toner materials as a proportion of the cleaning liquid by weight.

6. A cleaning system according to either claim 1 or claim 2 wherein said carrier liquid is Isopar.

7. A cleaning system according to claim 2 also comprising means for utilizing the filtered cleaning liquid for wetting said photoconductor surface.

8. A multi-color liquid toner electrophotographic system comprising: a photoconductive surface; means for providing a toner image on said photoconductor surfac ; means for transferring said toner image from said photoconductor surface onto a substrate; and means for wetting the photoconductor surface with a cleaning liquid comprising a essentially unpigmented carrier liquid which contains a lubricant.

9. A system according to claim 8 and also comprising: means for filtering the cleaning liquid downstream of the photoconductor surface to remove most of the solid 5 material from the cleaning liquid.

10. A system according to either claim 8 or claim 9 and wherein said lubricant is selected from the following: lecithin, Basic Barium Petronate, a charge director or a silicone material.

10 11. A system according to claim 9 wherein said means for filtering retains up to 0.1% of solid toner materials in the cleaning liquid.

12. A system according to claim 8 wherein said lubricant comprises up to 0.1% of solid toner materials as a

15 proportion of the cleaning liquid by weight.

13. A system according to either claim 8 or claim 9 wherein said carrier liquid is Isopar.

14. A system according to claim 9 also comprising means for utilizing the filtered cleaning liquid for wetting said

20 photoconductor surface.

15. A cleaning method for a liquid toner electrophotographic system including a photoconductor surface, the cleaning method comprising the step of: wetting the photoconductor surface with a cleaning 25 liquid comprising an essentially unpigmented carrier liquid containing a lubricant.

16. A cleaning method according to claim 15 and also comprising the step of: filtering the cleaning liquid downstream of the 30 photoconductor surface to remove most of the solid material from the cleaning liquid.

17. A cleaning method according to claim 16 wherein said step of filtering retains up to 0.1% of pigmented toner materials in the cleaning liquid.

35 18. A cleaning method according to claim 15 also comprising the step of utilizing the filtered cleaning liquid for wetting said photoconductor surface.

19. A multi-color liquid toner electrophotographic method comprising the steps of: providing a toner image on a photoconductor surface; 5 transferring said toner image from said photoconductor surface onto a substrate; and wetting the photoconductor surface with a cleaning liquid comprising a essentially unpigmented carrier liquid which contains a lubricant. 10 20. A method according to claim 19 and also comprising the step of: filtering the cleaning liquid downstream of the photoconductor surface to remove most of the solid material from the cleaning liquid. 15 21. A method according to claim 20 wherein said step of filtering retains up to 0.1% of solid toner materials in the cleaning liquid. 22. A method according to claim 19 also comprising the step of utilizing the filtered cleaning liquid for wetting 20 said photoconductor surface.