Cleaning unit

1. A method for removing debris particles from a LEP ink transfer surface, the method comprising:

providing a cleaning roller comprising a microcellular material outer layer comprising open cell pores having a diameter smaller than the particle size of the debris particles;

contacting the microcellular material outer layer of the cleaning roller with a LEP ink transfer surface to transfer debris particles from the LEP ink transfer surface to the cleaning roller;

wetting the cleaning roller with a cleaning fluid; and

removing cleaning fluid and debris particles from the microcellular material outer layer of the cleaning roller;

wherein both the wetting with cleaning fluid and removing the cleaning fluid from the cleaning roll occur away from and subsequent to contact with the surface being cleaned in a direction of rotation of the cleaning roller.

2. A method according to claim 1 , wherein wetting the microcellular material outer layer of the cleaning roller with a cleaning fluid comprises directly applying cleaning fluid to the cleaning roller.

3. A method according to claim 1 , wherein contacting the microcellular material outer layer of the cleaning roller with a LEP ink transfer surface comprises moving the cleaning roller from a non-contact position to a contact position such that the microcellular outer layer of the cleaning roller contacts the LEP ink transfer surface.

4. A method according to claim 1 , wherein removing cleaning fluid and debris particles from the microcellular material outer layer of the cleaning roller comprises providing a vacuum source to generate a pressure gradient such that debris particles and cleaning fluid are sucked away from the microcellular material outer layer of the cleaning roller.

5. A method according to claim 1 , comprising contacting the cleaning roller with the LEP ink transfer surface such that the cleaning roller is compressed against the LEP ink transfer surface.

6. A method according to claim 1 , wherein the LEP ink transfer surface is a photoconductive surface.

7. A method according to claim 1 , wherein the open cell pores of the microcellular material outer layer have a diameter of less than about 50 μm.

8. A method according to claim 1 , wherein the debris particles comprise fused LEP ink particles.

9. A cleaning unit for removing debris particles from a LEP ink transfer surface, the cleaning unit comprising:

a cleaning roller comprising a microcellular material outer layer comprising open cell pores having a diameter smaller than the particle size of the debris particles;

a wetting module to supply cleaning fluid to the cleaning roller; and

an extractor to remove cleaning fluid and debris particles from the cleaning roller.

10. A cleaning unit according to claim 9 , wherein the wetting module comprises a cleaning fluid duct for directly supply cleaning fluid to the cleaning roller.

11. A cleaning unit according to claim 9 , wherein the extractor comprises an extractor duct through which debris particles and cleaning fluid are removed from the microcellular material outer layer of the cleaning roller.

12. A cleaning unit according to claim 11 , wherein the extractor duct is in fluid communication with a vacuum source to generate a pressure gradient to remove debris particles and cleaning fluid from the microcellular material outer layer of the cleaning roller.

13. A cleaning unit according to claim 11 , wherein the extractor comprises a scrubber positioned within the extractor duct and engageable with the cleaning roller to aid removal of debris particles from the cleaning roller.

14. A cleaning unit according to claim 9 , wherein the open cell pores of the microcellular material outer layer have a diameter of less than about 50 μm.

15. A cleaning unit according to claim 9 , wherein the microcellular material has an Asker C hardness in a range of 10-20.

16. A cleaning unit according to claim 9 , wherein the microcellular material outer layer of the cleaning roller is disposed over a separate sponge inner layer of the cleaning roller.

17. A cleaning unit according to claim 9 , wherein the cleaning roller comprises a non-porous cylindrical core over which the microcellular material outer layer is disposed.

18. A cleaning unit according to claim 9 , wherein the extractor comprises a vacuum chamber with a number of spaced vacuum nozzles, wherein the vacuum chamber has a waved form in that a distance between a vacuum nozzle and the surface being cleaned is less than a distance between points on a wall between the vacuum nozzles and the surface being cleaned.

19. A cleaning unit according to claim 9 , wherein the extractor leaves some cleaning fluid on the LEP ink transfer surface, the cleaning unit further comprising a wiper blade to further wipe the cleaning fluid on the LEP ink transfer surface as the LEP ink transfer surface leaves the cleaning unit.

20. A liquid electrophotographic (LEP) printing apparatus comprising:

a LEP ink transfer surface; and

a cleaning unit for removing debris particles from the LEP ink transfer surface, the cleaning unit comprising:

a cleaning roller comprising a microcellular material outer layer comprising open cell pores having a diameter smaller than the particle size of the debris particles, the cleaning roller contactable with the LEP ink transfer surface;

a wetting module to supply cleaning fluid to the cleaning roller; and

an extractor to remove cleaning fluid and debris particles from the microcellular material outer layer of the cleaning roller;

wherein the extractor comprises an extractor duct through which debris particles and cleaning fluid are removed from the microcellular material outer layer of the cleaning roller; and

wherein the extractor comprises a scrubber positioned within the extractor duct and engageable with the cleaning roller to aid removal of debris particles from the cleaning roller.