photo polymer colour separation

Sorry but I’m a bit confused. What does “each layer off-setting from paper to plate” mean? When printing the second color was the plate picking up we ink from the paper?

What order are you printing in?
Typical is KCMY

Are you using process inks specifically for process printing?
A process set of ink, at least for offset, will have varying tacks so as not to pull the previous color off the sheet as well as they have the proper amount of transparency so the other color can show through them to some degree. Being that offset lays down a very very thin film of ink on the paper you’ll have to run far less ink than what your used to for letterpress.

yes, the second plate and the third and the fourth picks up the ink from the paper. sorry if I confused you.

I’m using process intaglio inks for the process as it’s a polymer gravure plate rather than a letterpress relief plate. I think I have to play around with the transparency and the tack as you suggested…and maybe the exposures and/or the curves on each layer.

would KCMY be the same sequence here? I tend to go ymck, but that’s for screen.

thanks for your help

…are you letting the ink dry between plates?

I’m not but I know that would help alot if the only problem to get around would be the re dampening of paper and paper stretch. I have a few options to try….print 2 plates then let dry then print the other two. or as you suggested, let ink dry between all four plates.
the files haven’t been adjusted digitally to compensate for dot gain so relying on exposure and the translucency of ink to control the colour.

I’m a technician with experience of polymer but not four colour separations and determined to crack this!

If you’re “wet trapping” (not letting the ink dry between colors), you have to do as is done with four-color presses and have a series of inks that each have less tack than the previous color. Whether you run YMCK, KCMY, or some other sequence won’t matter as far as printing (although it may affect the appearance of the finished piece), but you need to decide on a sequence and get inks with tack specifically for that sequence. If you’re running YMCK, for instance, the yellow must have the most tack, the magenta slightly less, the cyan less again, and the black the least tack.

If you try to print an ink with more tack on top of (wet) ink with less tack, the stickier ink will indeed simply pull some of the previous ink off the paper.

Dave (the Ink in Tubes guy)

cheers dave. is there such a thing as tack reducer or tack increaser for etching inks as they’re shorter/smoother than litho inks?

Lesley

could I use a number 7 litho varnish to add tack and/or easy wipe to make the other inks shorter.

so many possibilities!

Lesley, I’m afraid I know next to nothing about etching inks so I’m not sure about additives for them, but I would suspect that tack reducer should work the same way (even if it was made for litho ink), and adding a sticky varnish couldn’t help but increase the tack. Not as scientific as buying inks with a specific tack, but cheaper and perhaps more fun!

If you have good relations with a local ink manufacturer perhaps you could ask them for suggestions or advice.

Dave

cheers dave, I’ll give it a go.

thanks for your advice!

Lesley

Lesley, have you resolved this yet?

You don’t want to let the paper dry between printing. In fact, you should have all four (or however many) plates ready when you start printing.

I’d suggest you check pressure of your press and amount of moisture of the paper. If you can wipe the plate well, I don’t know that the consistency of the ink should be a factor, but who knows?

In general, intaglio printing ‘imbues’ the paper with ink (among the paper fibers, as opposed to just sitting on top of the paper), so it should not come up with another plate being printed. Maybe your paper is too damp or too dry so its not letting the ink find its way into the paper fibers? Just a guess.

Also, I’d work at getting the registration right, not compensating for it in how you print your separations. I know of a pretty simple but effective registration system I can share with you if you want. Let me know.

If you’re having trouble with paper stretching, you might try ‘calendaring’ first: running the paper a few times through the press under pressure, to sort of ‘stretch’ it out before you print.

Which inks are you using? which paper, which press?

Best, David

try adding dryer

I understood your problem, you should check out your substrate,which GSM you are using and coated or uncoated.
Because,Letterpress inks are mainly dry by absorption or penetration on paper.

you can also add some solvents with the ink to reduce viscosity and tackiness.

Very Important to dry enough polymer plate with Heat and should allow Post exposure when processing.

Palani
India