Flexo Screen Angles

[shorty83]

Do most of you use one common set of screen angles for all jobs? I know different screen angles produce different results depending on anilox angles. I had a job plated recently with a different set of screen angles than our "norm" and the dots ended up printing 100x better. I have used the same set for the last 14 years but now am considering switching. What I currently use is:
C: 7.5
M: 67.5
Y: 22.5
K: 37.5

New angles tried were:
C: 22
M: 52
Y: 7
K: 82

Is what I have been using wrong?

 

[gordo]

Do most of you use one common set of screen angles for all jobs? I know different screen angles produce different results depending on anilox angles. I had a job plated recently with a different set of screen angles than our "norm" and the dots ended up printing 100x better. I have used the same set for the last 14 years but now am considering switching. What I currently use is:
C: 7.5
M: 67.5
Y: 22.5
K: 37.5

New angles tried were:
C: 22
M: 52
Y: 7
K: 82

Is what I have been using wrong?

Yes. You were using the wrong screen angles.

Normally one uses the standard CMYK screen angles for flexo: Y@0°, C@105°, M@75°, K@45° (i.e. each screen is 30° away from the other except for Y which is 15° away). However if you’re running with 45° or 60° anilox rollers you must avoid using the same angle as the anilox. This is usually accomplished by rotating those screens by 7.5°.

So your old angles (minusing their 7.5° rotation to make things more clear) are:
C 0°
M 60°
Y 15°
K 30°

They don’t meet the correct screen angle requirements.

Your new angles

C: 22
M: 52
Y: 7
K: 82

Better meet the screen angle requirements so they should provide a better result.

Normally the darkest color screen angle (K) should be closest to 45° which is the least visible screen angle. And the lightest color screen angle (Y) should be closest to 0° which is the most visible screen angle.

 

[shorty83]

Thanks for the info, if the angles I have been using for the last 14 years are wrong I am confused as to why there was never and issue. Also, my current angles are all 30° apart (except for the yellow) so why wouldn't they meet the requirements?

If I switch to different screen angles and the darkest should be closest to 45 should it be this way?:

C: 82
M: 22
Y: 7
K: 52

 

[gordo]

Thanks for the info, if the angles I have been using for the last 14 years are wrong I am confused as to why there was never and issue.

You did say "I had a job plated recently with a different set of screen angles than our "norm" and the dots ended up printing 100x better." So there apparently was an issue or at least the results weren't optimal.

Also, my current angles are all 30° apart (except for the yellow) so why wouldn't they meet the requirements?

If I switch to different screen angles and the darkest should be closest to 45 should it be this way?:

C: 82
M: 22
Y: 7
K: 52

Pretty much right. If you follow FIRST guidelines for flexo (with the 7.5° offset) you'd be using:

C @ 82.5°
M @ 22.5° *
Y @ 7.5°
K @ 52.5°

Or

C @ 22.5° *
M @ 82.5°
Y @ 7.5°
K @ 52.5°

The Y screen being offset by its neighbour by only 15° always moirés. But because Y is such a light color, relative to the color it's 15° offset from, you typically don't see the moiré. If the Y ink gets contaminated or is too dark the the moiré will be visible. Vendors also typically set the Y screen lpi at about 108% of the C, M, and K screens to make the moiré pattern frequency greater and hence less visible. So, the C and M angles can be swapped depending on they type of work you do i.e. what colors you print that have the greatest likelihood of moiré due to the Y printer.

* On a sidebar - Due to the quadratic symmetry of halftone screens, screen angles like 0°, 90°, 180°, and 270° are identical - i.e. they are all the same screen angle. When looking at screen angles, especially if they appear to be run at some exotic angles, it helps to add or subtract 90 from the stated angle to figure out how the angles relate to the industry standard.