Printing PMS screens

[PA Printer]

When we print certain PMS colors (dark blues, dark greens, grays, browns, etc.)to match density of Pantone swatches, the ink film is so heavy that our screens fill in and look terrible, especially screens of 70% and up. We have tried reducing the line screens and sometimes the screen percentage but this seems like we are just putting a bandaid on it. Sometimes we can add black ink to the mix and run a lighter film of ink which helps but this is does not work with all colors. We also have tried new blankets and even switched to different fountain solution. Still no luck. This occurs on both coated and uncoated stocks. Any other suggestions?

[Cornishpastythighs]

I think this is a common problem especially with packaging printing where you are trying to lay down a nice solid ink film to cover up the hills and valleys in the stock and keep hickeys away but also expected to produce fine screen dots all from the same plate. If you have enough print units you can print the PMS screens in one unit and the PMS solids in another unit. I have seen different ink manufacturers produce dramactically different results when printing dark solids and screens on from the same plate. Its a difficult balancing trick to produce a dark blue that has a Pantone ink density reading of 2.00 and still hold fine screens open.
I would also be very interested to hear of anyone who has 'mastered' this.

[gordo]

As a general rule - Pantone spot color inks are not formulated by the ink vendor to be halftone screened nor wet trapped. Typically the pigment load/dispersion is such that if you screen the spot color you'll see wildly varying dot gains, ink transfer qualities, and graininess in screened areas. If you can take a micro-photograph and post it (and compare it with your process colors) you might see if that's the problem.
Are you using a plate curve to normalize the dot gain? Some printers use the black plate cure for spot colors, others use the plate curve of the process color that is most similar in darkness to the spot color. Some printers build custom curves.
Do you inform your ink supplier about how you're going to use the spot color? They can usually formulate the ink accordingly.

best, gordo

[Richard]

My first thought with your concern printing screened area is:
Your swatch is solid. So you can't match it unless you remove the screen
and print solid. Running the screen as dark as possible before plugging
in is a matter of the competence of your pressman, precision, and condition
off your press, and of course the condition of your plate. Running a 80-90% screen is possible, but not recommended.

[TheProcessIStheproduct]

just have to make a real extreme tone rep curve for those dark spot colors, to hold a 90% of reflex blue it is going to have to really be a big adjustment

[chevalier]

We use Cyan as our standard plate curve for spot colors. We run into this problem a lot. We have gone to the trouble of creating curves for many of our common spot colors. It really isn't too big of a deal to make a custom color bar and to measure it and program it into your RIP. It will save your press operators and prepress guys a lot of hell and prevent a lot of shooting in the dark.