CHROMiX

CTP correction curve for PVC + Varnish

I’m trying to make CTP compensation curves to bring our PVC in line with ISO39L. Now I realise that this standard isn’t specified for use with this substrate, but then again there is no standard that is, as far as I know. Resulting corrections are taking massive amounts of dot out of our plates and I think this is causing a problem where to an extent the ink is still spreading too much and negating the work that the curve is doing. My idea is to take work out of the job at file stage so that the plate curve doesn’t have to work so hard.

Any ideas? My Minders say they can’t adjust ink/water settings (I figured that they needed to make the ink thicker perhaps)

G7 calibration method has worked very well for targeting GRACoL 2006 specification on PVC. We have done several PVC and PET calibrations with UV conventional ink sets and UV waterless ink sets with great results.

Problems causing TVI shifts for us were inconsistent press conditions, inconsistent PVC thickness, and incorrect PVC storage temps and humidity. There can be variation in substrate thickness depending on the PVC extruder who should tell you their standard tolerance. Ambient temperature and humidity when storing PVC does effect print characteristics and may cause a variety of quality issues including TVI going up or down.

You can come close or even hit ISO 12647-2:2004 solids and 2 color overprint color aims if your ink set is close or certified ISO 2846 and the PVC is relatively close to neutral. And then achieve gray balance and weight with the G7 method.

BUT MOST IMPORTANTLY FOR US, process control of substrate and press must to be strict to keep you from making job-to-job correction curves.

Hi K2RUM,

I think you can can achieve your desired result without editing the files to make the CTP curves less dramatic. I would not take the path of doing an ‘extra image edit’. Well, there would be a lot of fighting before I did.

All about process control Mate, I agree with Jeff that G7 is probably going to be your best bet. The G7 profile, Gracol2006 is based on exactly the same press run data as ISO39L - using ‘non-standard’ variables with G7 methodology will get you absolutely knocking on the door of an ISO Coated V2/Fogra 39 proof. I have used dramatically non standard UV inks on a KBA 162 printing fashion posters and had a result that looked ‘exactly’ like the ISO Coated/Fogra 39 proof (except the proof was much, much smaller!).

Your situation sounds a lot like the flexo world - in which i also thrive :slight_smile:. In Flexo you really need to make sure every possible variable is ‘in tolerance’. You may still be required to give the CTP curves a hefty shove to get what you want - but is it possible even using different hue inks on different substrates to get a fairly ‘close visual match’ to a Gracol2006/ISO Coated V2 proof (gamut permitting).

While your Minders say they can’t adjust ink/water, I don’t believe them! Roller nips, plate pressure, blanket pressure, ink tack etc. A lot of the answer lies in the press-room.

I’ll bet if you start documenting press variables as seen in the G7 PreQualification Kit it would change your situation for the better. It can take a while, but you can get there.

Best regards,

Dan Wilson
Dublin, Ireland

Dan, I didn’t say I believed them :slight_smile:

Thanks for the advice both of you. I agree that adjusting the file is a last resort but I admit I was a bit stuck for where to go from here. You have given plenty of food for thought though. Never considered the G7 method.