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The relationship between ink and water is deep and complex, with analysis by CRC uncovering some surprising results. This month we return to some of the fundamental work being undertaken by the Smartprint research centre, this time into the mechanics of the lithographic process itself.

I wrote last year about the work that is being overseen by Dr Shen of the Chemical Engineering department at Monash University into the complex relationships of litho ink, fountain solution and plate surfaces, and now as the work progresses, it is time to detail some more discovery from that remarkable research team.

We all know that it is essential to have a continuous film of fountain solution on the non-image surface of the litho plate to prevent ink from spreading into the areas not intended to transfer, but many questions have remained unanswered (or unasked) as to how the system really works.

If we believe the simplistic hypothesis that says because the image area is hydrophobic and the non-image area is hydrophilic, (and ink and water do not mix), it is surface tension that separates non-image from image - why does ink turn up in the non-image areas at all, and further, why is it that when a plate is first dampened, the fountain solution film extends over the entire surface?

In order to test out the surface tension theory, Dr Shen set up a very elegant experiment where he made printing blocks from ice (solid water of about the same surface tension as the liquid variety), and used these blocks to quite happily print conventional litho news inks. He also noted that as the temperature of the iceblocks rose, the ability of the type to print decreased proportionally.

For a detailed explanation we must briefly refer to some physics.

To quote directly from Dr Shen, "An important question of the fundamental mechanism of lithography is whether the splitting (the transfer of ink) occurs at the fountain solution/ink interface, or within the fountain solution layer".

Naturally we would believe that the strength of the aqueous layer would always be weaker than that of the ink, but think again. It has been on the record (for around 30 years) that cleavage along the interface between two phases is highly improbable; instead failure almost always occurs within one of two phases.

Fountain solution, as we well know, is predominantly water, and it is the behaviour of water at low temperatures that explains the iceblock effect, and ultimately how litho really works.

The 19th century scientist Michael Faraday first proposed that a very thin layer of liquid-like material covered the surface of ice (which makes ice slippery). Subsequent studies have shown that the thickness of the liquid-like layer varies with temperature.

At temperatures below -5 degrees Celsius, the thickness of the liquid layer is less than 10 nanometres, but is equal to or greater than 10 nm at or above zero.

Attraction
And now for a piece of real physics. At very small distances, an effect known as the van der Waals force/interaction occurs that is responsible for adhesion and attraction between materials. These forces become greater the smaller the separation between molecules becomes. This explains the iceblock result, as at a very thin liquid layer, ink stuck to the ice and transferred (split) to paper, but as the ice became coated with a thicker layer of liquid, the transfer stopped as the water layer did the splitting.

Extrapolating from this experiment to the surface of the plate in a press, a very thin layer of water on a litho plate would require gigantic force to split - hugely greater than the cohesive forces holding an ink together. Under these conditions, splitting would occur within the ink layer, which now becomes the weak link, and so ink would transfer to the supposedly wet area of the plate.

As the thickness of the water film increases above the distance over which the van der Waals force operates, the ink becomes the stronger link and so would rather cohere to itself rather than stick to the wet non-image area.

Think about the opposing causes of catchup and washout, and it all makes fine sense.

To close on a topical note, PacPrint provided a most welcome opportunity for me to meet with many old friends from the industry as well as the chance to see the fine equipment and systems on show. In particular the wide format ink jet printers were quite remarkable in their ability to print exceptional quality on a most varied range of substrates.

Another highlight of the PacPrint week was the National Print Awards ceremony at the Crown Palladium. The capacity audience of over 1250 illustrated the eminence of the program, and the value that the industry places on the awards themselves.

The release of the Design for Print (D4P) manual at the National Printing Laboratory stand has a coincidental linkage to the Print Awards, as it was following the 2004 judging, a chance remark I made set the wheels in motion that culminated in the publication of the useful D4P guide.

The comment was that among the print work adjudicated by the judging panel, many otherwise fine examples of printing were so handicapped by the demands of design; the printerÂ’s task to produce a perfect result was made near impossible.

I cited cases where fine lines were made up of four-colour process inks, and page numbers were reversed out of multicolour blacks and browns, an undertaking simply beyond the limitations of the printing process to maintain register. Similar design faults like halftone illustration surrounded by solid colour, geometric reverse areas in solids, and other clunkers were added to the discussion, at the end of which, our Smartprint Communications Manager, Astrid Sweres, said, "Why don’t we write this down and tell designers what not to do?" And as the saying goes, the rest is now history.

The resulting manual is a distillation of literally decades of experience, and provides straight forward explanations and tips to print designers on how to blend their talents with those of printers to avoid the development of creations that may look sensational but are simply impractical to print. Copies of D4P are currently available through the National Printing Laboratory.