Red ink trapping - help pl

[ganesh]

Dear Friends,

Kindly clarify the following.

When i print a test chart and convert my press to ISO 12647 - 2 standards (for ex: paper type 1, gloss paper), and print again with standard densities, i always get my red trapping less than 70% (recommended is minimum 75%). Why is it happening.

I'm using GMG Printcontrol pro to standardise the press.

Regards,

ganesh

 

[shajith]

hi ganesh good to see you on this forum.
regards shajith

 

[Lukas Engqvist]

If Trapping is not correct it is a press, or ink problem. Could be a problem with fount soloution. Red trapping means the yellow is not printing on top of magenta. If your green trapping is OK then magenta is what needs a closer look? (I'm not press, but I over hear some ;p)

You should be able to get guidance from your ink supplier. I would also advice posting in the inks forum, since there may be printers that are not into color management but still very knowlegable in trapping inks.

 

[LSW]

Are you running correct ink sequence, K/C/M/Y?

 

[ganesh]

Hi,

The sequence is KCMY only.

For R&D, we tried a sequence of MCYK also. Even then the trapping is poor. As other friends have rightly said, i'm in discussions with Ink manufacturers.

Regarding fountain solutions and other variables etc, I have tested in 12 machines of all mades, but i get the same trapping results.


ganesh

 

[Lukas Engqvist]

Have you calibrated your equipment? I was at a company where densities from different meassuring devices varied one showing 1.5 the other 1.3 when measuring C and M. Check the expiry date of the calibration card.
You may have ruled this out already, since it is a basic step. (We have had to change our stripreading densitometer twice due to bad readings)

 

[pressman.in]

Hi Ganesh,
If your green trapping is good, then look for yellow shade. There are differenet yellow shades like golden yellow /lemon yellow (process yellow colors). Check with the ink manufacturer about their trap value and then try with other color shade. Also take magenta and yellow sheets separately without trapping and measure the density of both .

 

[otherthoughts]

Hi,

The sequence is KCMY only.

For R&D, we tried a sequence of MCYK also. Even then the trapping is poor. As other friends have rightly said, i'm in discussions with Ink manufacturers.

Regarding fountain solutions and other variables etc, I have tested in 12 machines of all mades, but i get the same trapping results.


ganesh

Ink trapping is affected by ink sequence, ink tack, press interval(the distance between impression units), press speed and the substrate(paper/stock)absorbency to name just a few.

The change in rotation from KCMY to your R&D-MCYK rotation effectively doubles the press interval between the first down magenta ink and the second down yellow ink and should normally have made a difference in the yellow ink being trapped more completely by the magenta ink.

Typically the first down ink increases in tack with time after being transferred to the substrate. By doubling the press interval, you doubled the time between these two inks. In other words, with enough time you move from a wet trap to a dry trap. This is also why press speed influences trapping as well.

As others have suggested in this thread, check the accuracy of your monitoring equipment and work with your Ink Supplier. Bear in mind that improving the efficiency of the yellow ink being captured/trapped by the magenta ink might result in problems appearing elsewhere.

Best Regards
Otherthoughts