Digital printing process and system
Embodiments of the invention relate to a method of indirect printing with an aqueous ink. In some embodiments, an intermediate transfer member (ITM) comprising a silicone-based release layer surface is employed. For example, the release layer surface satisfies at least one of the following properties: (i) a receding contact angle of a drop of distilled water deposited on the silicone-based release layer surface is at most 60°; and (ii) a 10-second dynamic contact angle (DCA) of a drop of distilled water deposited on the silicone-based release layer surface is at most 108°. Related apparatus, systems and treatment formulations are disclosed herein.
1. A printing system comprising:
a. a rotatable intermediate transfer member (ITM);
b. an image forming station configured to form ink images upon a surface of the ITM, as the ITM rotates;
c. an impression station disposed downstream of the image forming station and configured to transfer the ink images from the ITM surface to substrate; and
d. a treatment station configured to apply, as the ITM rotates, a liquid to a surface of the ITM to form a liquid-coating on the surface of the ITM, the treatment station being disposed downstream of the impression station and upstream of the image forming station, the treatment station comprising:
(i) a bar having a channel disposed at one end thereof, and
(ii) a rod supported by and/or at least partially disposed in the channel, wherein a portion of a surface of the rod is rounded and faces the ITM surface,
wherein rotation of the ITM moves the applied liquid along a direction-of-rotation of the ITM, and wherein a presence of the rod deflects some the moving liquid away from the ITM surface, thereby thinning the liquid-coating of liquid, and
wherein the system is configured such that at least one of a first condition and a second condition is true, and wherein the first and second conditions are defined as follows:
(I) according to the first condition, a presence of the liquid-deflecting rod thins the liquid-coating of liquid down to a thickness that is at most 0.8μ;
(II) according to the second condition, rotation of the ITM moves the surface of the ITM at a surface-velocity of at least 1 meter/second.
2. The system of claim 1 , wherein the bar is oriented normal to a portion of the ITM surface that is opposite to and that faces the ITM-facing portion of the rod surface.
3. The system of claim 1 , wherein the rounded tip is urged towards the ITM surface or wherein the rounded tip and the ITM surface are urged towards each other.
4. The system of claim 3 , wherein the ITM-surface-facing rounded-portion of the rod is urged towards the ITM surface or wherein the ITM-surface-facing rounded-portion of the rod and the ITM surface are urged towards each other, by a backing roller having a soft outer surface.
5. The system of claim 1 wherein a magnitude of a gap between the ITM surface and the ITM-surface-facing rounded-portion of the rod regulates an extent of thinning the in-motion layer of liquid.
6. The system of claim 1 wherein a post-thinning thickness of the in-motion layer of liquid is equal to a magnitude of a gap between the ITM surface and a location on the ITM-surface-facing rounded-portion of the rod.
7. The system of claim 2 wherein respective central axes of each of the channel and the rod are oriented parallel to the portion of the ITM surface that is opposite to and that faces by the ITM-facing portion of the rod surface.
8. The system of claim 7 wherein the ITM comprises an endless belt defining longitudinal and lateral directions, and wherein said respective central axes of each of the channel and the rod are laterally oriented with respect to the endless belt.
9. The system of claim 1 wherein respective central axes of each of the channel and the rod are oriented parallel to the portion of the ITM surface that is opposite to and that faces by the ITM-facing portion of the rod surface.
10. The system of claim 9 wherein the ITM comprises an endless belt defining longitudinal and lateral directions, and wherein said respective central axes of each of the channel and the rod are laterally oriented with respect to the endless belt.
11. The system of claim 1 wherein the rounded and ITM-facing portion of the rod surface is oriented perpendicular to a central axis of the rod.
12. The system of claim 1 wherein the rod is elongated to define an elongate-axis, and wherein the rounded and ITM-facing portion of the rod surface is oriented perpendicular to an elongate-axis of the rod.
13. The system of claim 1 wherein the liquid is an aqueous liquid.
14. The system of claim 1 , wherein at least the first condition is true.
15. The system of claim 1 , wherein at least the second condition is true.
16. The system of claim 1 , wherein both of the first and second conditions are true.
17. A method of printing comprising:
a. applying a liquid to a surface of a rotating intermediate transfer member (ITM) to form a liquid-coating on the surface of the ITM, wherein (i) the ITM comprises a flexible endless belt mounted over a plurality of guide rollers; and (ii) rotation of the ITM moves the applied liquid along a—direction-of-rotation of the ITM;
b. deflecting, by a rod, some of the moving liquid away from the ITM surface so as to thin the liquid-coating, wherein:
i. the rod is supported by and/or at least partially disposed in a channel disposed at one end of a bar; and
ii. a portion of a surface of the rod is rounded and faces the ITM surface;
c. subsequently, depositing droplets of ink onto the ITM surface to form thereon an ink image; and
d. transfer ink image to substrate,
wherein the method is performed such that at least one of a first condition and a second condition is true, and wherein the first and second conditions are defined as follows:
(I) according to the first condition, the deflecting of step (b) is effective to thin the liquid-coating down to a thickness that is at most 0.8μ;
(II) according to the second condition, rotation of the ITM moves the surface of the ITM at a surface-velocity of at least 1 meter/second.
18. The method of claim 17 , performed such that at least one of a third condition and a fourth condition is true, and wherein:
A. according to the third condition, the rod is adhesively retained with the channel of the bar; and
B. according to the fourth condition, the rod is retained, by friction, within the channel of the bar.
19. The method of claim 17 , wherein the bar is oriented normal to a portion of the ITM surface that is opposite to and that faces the ITM-facing portion of the rod surface.
20. The method of claim 19 wherein respective central axes of each of the channel and the rod are oriented parallel to the portion of the ITM surface that is opposite to and that faces by the ITM-facing portion of the rod surface.
21. The method of claim 20 wherein the ITM comprises an endless belt defining longitudinal and lateral directions, and wherein said respective central axes of each of the channel and the rod are laterally oriented with respect to the endless belt.
22. The method of claim 17 wherein respective central axes of each of the channel and the rod are oriented parallel to the portion of the ITM surface that is opposite to and that faces by the ITM-facing portion of the rod surface.
23. The method of claim 22 wherein the ITM comprises an endless belt defining longitudinal and lateral directions, and wherein said respective central axes of each of the channel and the rod are laterally oriented with respect to the endless belt.
24. The method of claim 17 wherein the rounded and ITM-facing portion of the rod surface is oriented perpendicular to a central axis of the rod.
25. The method of claim 17 wherein the rod is elongated to define an elongate-axis, and wherein the rounded and ITM-facing portion of the rod surface is oriented perpendicular to an elongate-axis of the rod.
26. The method of claim 17 wherein the liquid is an aqueous liquid.
27. The method of claim 17 , wherein at least the first condition is true.
28. The method of claim 17 , wherein at least the second condition is true.
29. The method of claim 17 , wherein both of the first and second conditions are true.