Intermediate transfer technology from Xerox

US 2015/0022605 A1
System and method for transfixing an aqueous ink in an image transfer system
EP 2 826 633 A1
System and method for transfixing an aqueous ink in an image transfer system
Xerox Corporation

Interest in intermediate transfer systems is high at present, no doubt as a result of the Landa Digital demonstrations at Drupa 2012. Xerox has for many years sold printers using intermediate transfer methods with phase change inks. But the goal here is to find a way of doing the same with liquid inks. It is also desirable to not involve heat for the transfer process if possible, as excessive temperature of the transfer substrate will shorten its life.

The intermediate transfer substrate needs to have properties that will allow the release of the ink film and its transfer to the substrate, yet the ink must wet it sufficiently on landing. Insufficient wetting results in ‘drawback’; at impact the drop is flattened, but then surface tension pulls the ink back into a drop.

The proposed solution is to coat the intermediate transfer substrate with a powder layer including an aggregation treatment agent capable of precipitating colorants, latex or resin in the ink drops.

Jan-15The particles are very small, 1-10 microns in diameter, and need to be coated uniformly and at uniform density on the substrate. Coverage of 5-40% is sufficient providing the particle distribution is uniform, so that many particles will be impacted by an individual drop.

Not surprisingly, considering Xerox’ background, methods of coating the powder include electrostatically biased rollers, brushes, and cloud development used in electrophotography. The particles contained metal salts, such as iron sulphate and copper sulphate. These are combined with other materials to form the powder.

As the drops impact the powder the colorant or pigment begins to precipitate out of the ink due to the aggregation agent in the particles. As the process continues a coating of pigment and resin is formed on the substrate surface. This causes further diffusion of the aggregation agent into the drop, and also prevents the drawback of the ink. Examples shown and discussed in the patent use 14 pl drops printed on to a silicon plate as the substrate.