Fog development for digital offset printing applications
Ink-based digital printing systems useful for ink printing include a photoreceptor layer configured to receive a layer of liquid immersion fluid. The liquid immersion fluid includes dampening fluid, dispersed gas particles, and charge directors that impart charge to the solid particles. The photoreceptor surface is charged to a uniform potential, and selectively discharged using an ROS according to image data to form an electrostatic latent image. The charged liquid immersion fluid adheres to portions of the photoreceptor surface according to the electrostatic latent image to form a fountain solution image. The fluid portion of the fountain solution image can be partially transferred to an imaging member and/or transfer member to form a dampening fluid image, either or both of which may be electrically biased. The dampening fluid image is inked on the transfer member, and the resulting ink image transferred to a print substrate.
1. An ink-based digital printing system useful for ink printing, comprising:
an imaging member configured for carrying a fountain solution image on the imaging member;
an image forming unit that forms an electrostatic charge image of a first polarity on a surface of the imaging member;
a developer unit proximate the imaging member and adapted to form a fog of charged droplets that are attracted to the electrostatic charge image to form the fountain solution image on the imaging member; and,
an inking system, the inking system being configured to apply ink to produce an inked image according to the formed fountain solution image; and
an ink transfer nip for transferring the inked image to a receiving medium.
2. The system of claim 1 , further comprising:
wherein the inking system applies ink to the imaging member according to the fountain solution image on the imaging member to produce the inked image;
an ink image transfer station positioned downstream of the inking system in a process direction that transfers the inked image to an image receiving medium substrate.
3. The system of claim 1 , further comprising:
a transfer member, forming a transfer nip with the imaging member, for splitting a controlled fraction of the fountain solution image onto the transfer member;
wherein the inking system applies ink to the transfer member according to the fraction of the fountain solution image on the transfer member to produce the inked image;
wherein the inked image is applied to the image receiving medium substrate.
4. The system of claim 1 , the developer unit further comprising:
an inlet for receiving a fountain solution and a discharge forming the fog of charged droplets, wherein the fog of charged droplets comprises multiple substantially uniformly sized electrically charged droplets of the fountain solution.
5. The system of claim 4 , the developer unit further comprising:
an outlet for clearing the fountain solution away from the developer unit.
6. The system of claim 4 , the developer unit further comprising:
a charged surface disposed proximate the discharge and along the fog of charged droplets to guide the charged droplets to the imaging member.
7. The system of claim 4 , further comprising:
a controller to create the fountain solution image on the imaging member with a desired thickness by controlling the image forming unit and the developer unit;
wherein the fog of charged droplets is attracted to the electrostatic charge until the fog of charged droplets neutralizes the electrostatic charge image on the imaging member.
8. The system of claim 4 , wherein the image forming unit is at least one of electrographic imaging system and ionographic imaging system.
9. The system of claim 8 , the fountain solution comprising:
a dampening fluid selected from the group consisting essentially of silicone fluids (including D4, D5, OS20, OS30), Isopar fluids.
10. The system of claim 7 , the imaging member comprising:
a surface selected from the group consisting essentially of silicone elastomers, fluorosilicone elastomers, and Viton.
11. The system of claim 10 , wherein the developer unit creates droplets from the fountain solution and suspends said droplets in a carrier gas to form the fog of charged droplets.
12. The system of claim 7 , wherein the fog of charged droplets consist of frozen particles.
13. A method of ink-based digital printing using fountain solution fluid, comprising:
forming a fountain solution image on an imaging member using an image forming unit and a developer unit, the developer unit being positioned proximate the imaging member and adapted to form a fog of charged droplets that are attracted to an electrostatic charge image to form the fountain solution image on the imaging member;
applying ink with an inking system to produce an inked image according to the formed fountain solution image; and,
transferring the inked image to a print substrate at an ink transfer nip.
14. The method of claim 13 , further comprising:
wherein the inking system applies ink to the imaging member according to the fountain solution image on the imaging member to produce the inked image;
transferring the inked image from the imaging member to a print substrate at a transfer station positioned downstream of the inking system in a process direction.
15. The method of claim 13 , further comprising:
splitting a controlled fraction of the fountain solution image onto the transfer member with a transfer member forming a transfer nip with the imaging member;
wherein the inking system applies ink to the transfer member according to the fraction of the fountain solution image on the transfer member to produce the inked image;
wherein the inked image is applied to a target image receiving print substrate.
16. The method of claim 15 , the developer unit further comprising an inlet for receiving a fountain solution and a discharge forming the fog of charged droplets, wherein the fog of charged droplets comprises multiple substantially uniformly sized electrically charged droplets of the fountain solution.
17. The method of claim 16 , the developer unit further comprising an outlet for clearing the fountain solution from the developer unit.
18. The method of claim 16 , the developer unit further comprising a charged surface disposed proximate the discharge and along the fog of charged droplets to guide the charged droplets to the imaging member.
19. The method of claim 18 , wherein the fog of charged droplets is attracted to the electrostatic charge until the fog of charged droplets neutralizes the electrostatic charge image on the imaging member.
20. The method of claim 16 , further comprising:
controlling the image forming unit and the developer unit to form the fountain solution image with a desired thickness.
21. The method of claim 16 , wherein the image forming unit is at least one of electrographic imaging method and ionographic imaging method.
22. The method of claim 21 , the fountain solution comprising:
a dampening fluid selected from the group consisting essentially of silicone fluids (including D4, D5, OS20, OS30), Isopar fluids.
23. The method of claim 22 , the imaging member comprising:
a surface selected from the group consisting essentially of silicone elastomers, fluorosilicone elastomers, and Viton.
24. The method of claim 21 , wherein the fog of charged droplets consist of frozen particles.
25. The method of claim 23 , wherein the developer unit creates droplets from the fountain solution and suspends said droplets in a carrier gas to form the fog of charged droplets.