Process Color Angles

[GV1200]

How do you decide what your process color angles should be? When do you decide to adjust them?

We are seeing to much magenta on black/grey gradients. After reading some other threads I feel a slight adjustment to the angle may be the fix but need more facts or opinions to get a better idea of what should be tried.

[exflexo]

It sounds to me that you need to adjust your cutback (press gain) curve and not your halftone screen angles. The angle of the screen has nothing to do with the amount of perceived or actual press gain. The screen angle can however cause a moire pattern if there is a conflict between the halftone angle and the angle of your anilox rolls.. but all modern anilox rolls have been angled so that pre-press could use conventional offset screen angles. With all that said it sounds like you need to adjust your midtone or 3/4 tone cutback. Whatever your cutback is now, I would cut it back further by another 10% in the mid-tone and another 5-7% in the 3/4 tone and run a test plate to verify.

BTW - I am assuming that your presses are well maintained and that you have characterized and optimized the printing conditions for each station... otherwise you will be chasing a moving target and repeatable improvement cannot be expected.

[Luc St-Pierre]

I agree with exflexo concerning adjusting cut back values. I generally use 68 for K, 8 for C, 83 for Y and 38 for M. The only danger with this set and any set in this range is a Yellow-Black moiré, those angles beeing only 15 degrees apart. If you happen to have a subject with K and Y predominant, the trick would be to use anti-moiré dotshape for yellow that comes with some RIP's or workflows or try to cheat on Y linescreen can do the trick.

[exflexo]

The other "trick" for avoiding that moire is to use 3 color process and only use black for the "skeleton" or very dark shadow and hard lines etc. Then you can have your CMY at opitmal angles and the black will not interfere with the yellow. Three Color Process is the way to go with many items, but press conditions must be tightly optimized and you must be able to print a consistent gray balance from your three color process... otherwise it can be a mess.

[prepressbb]

To exflexo: Hey there i'm new to the forum, but was referred here from a friend. Isn't there default angles to use for flexo..??

[NarrowWebGuy]

There are guidelines in FIRST 4.0 (section 15.3, "Image Screening"). You can modify them for special applications----some of these are listed in the document.

The general guideline is:
Black = 37.5 (assuming it is the dominant color)
Magenta = 67.5
Cyan = 7.5
Yellow = 22.5

http://www.flexography.org/edutrain/first.cfm

[kamran]

Hi,
How can I get FIRST 4.0? Is it a document that can be found somewhere?

[iLabels]

You can purchase the book at: http://www.ftastore.com/index.cfm?fusea ... egory_ID=2

[fcascardo]

I have a question thats around my head for some time, after I do my color separation in RIP, how do I know which anilox roll LPI/BCM to use for each separation? How do you select the anilox?

[SknyRussianHillbilly]

At one time rule the of thumb was 3 lpi (or cells per inch) engraving for every 1 lpi of halftone screen frequency.
At that time a 120 line process halftone would typically run on a 360 or 400 line anilox because that was high end on the engraving.
As the sciences of engraved rollers improved it moved to 4:1, then 5:1, and some even use 6:1.
The bottom line is that finer engravings seem to run cleaner, be less likely to produce plate plugging, and a type of dot gain.
There is a lot of sales hype on newer and different engravings, if you stick with the tried and true 60 degree engraving angle you should not be disappointed.
As far as cell volume or BCM goes they should be the same for all colors. Adjustments for strength values can ge made on the ink side. And the inks do need to be maintained for consistency.
The science of process printing is pretty good in flexo nowadays, but you need to do be able to do some measuring and testing ahead of time to make good use of those applications. They will likely involve your plate, anilox, and ink people to one degree or another. Name of the game is consistent repeatability.
I may guess that you could be "winging" a process job here and there. Skilled craftsmen with a 'bag of tricks' did it well for years. The best of them we may be thankful to for developing the sciences that can be found documented in nice publications like the aforementioned FIRST 4.0.
Good luck to you my friend.

[guy de cafmeyer]

Seeing too much colour in gradients / vignette is also related to compensation . Often a vignette is for example 30% up to solid . To compensate for a vignette one then takes the 30% value as 0 , and the solid as 100. Then compensate the "false" mid-tones to maintain good vignette . . make sense ?