White Screen Angle

I need to print a white ink gradient under a 4/C process screen on silver substrate. Any suggestions on a screen angle for the white?
We are a flexo shop so our current cmyk angles are:
C=67.5
M=7.5
Y=22.5
K=37.5

I know that 52.5 won't work (it creates a pattern)
Any input would be appreciated
Thanks
 

gordo

Well-known member
I need to print a white ink gradient under a 4/C process screen on silver substrate. Any suggestions on a screen angle for the white?
We are a flexo shop so our current cmyk angles are:
C=67.5
M=7.5
Y=22.5
K=37.5

I know that 52.5 won't work (it creates a pattern)
Any input would be appreciated
Thanks

You're using standard screen angles (30° offsets with 15° for the Y)
I'm not sure why 52.5 didn't work because it is the same 15° offset (from K) as Y. If Y doesn't create a pattern then I would try the Y angle at 22.5 for the white. I.e. run both Y and W at the same angle. Possibly run it at a slightly higher or lower lpi than the Y (about 10% difference)

best gordon p
 
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dabob

Well-known member
What I have done in the past for this issue to to rip the gradient in Photoshop to a very hi rez (1200 dpi) greyscale image then covert to a bitmap using the diffusion dither then place in the correct position and give it the spot color white - no screen necessary or as a more conventional option give it a different line screen than the cmyk plates - different line count = no morie pattern . ..
 

gordo

Well-known member
What I have done in the past for this issue to to rip the gradient in Photoshop to a very hi rez (1200 dpi) greyscale image then covert to a bitmap using the diffusion dither then place in the correct position and give it the spot color white - no screen necessary or as a more conventional option give it a different line screen than the cmyk plates - different line count = no morie pattern . ..

Since this is flexo, a first order FM screen (PShop's diffusion dither) would be problematic for plate imaging.

best gordon p
 
Thanks for the input. Gordo, I'm afraid that putting the white at the same angle as yellow, at some point the dots will line up and the yellow will be seen above all other colors. I may try using the yellow angle at a different line screen per dabob.
My next question is, has anyone tried this method? I have no way to proof the white on silver substrate to see the results, so have to get it right the 1st time.
 

Rick@IPCO

Member
Are you using negative or positive plates? Is the 4-color process also a gradient (is the white serving as a base for a process gradient)? This might sound silly because I'm just grasping at straws but, could you burn all four process colors (or just the white), at all four angles, on the same plate to make up the white? I think that could technically be done on a negative plate.
 

gordo

Well-known member
Thanks for the input. Gordo, I'm afraid that putting the white at the same angle as yellow, at some point the dots will line up and the yellow will be seen above all other colors. I may try using the yellow angle at a different line screen per dabob.
My next question is, has anyone tried this method? I have no way to proof the white on silver substrate to see the results, so have to get it right the 1st time.

The Y is typically run at 108% of the lpis of the CMK lpi. Which is why I also suggested that you run the white at a slightly higher or lower lpi.
Y always has screen angle moiré because it is only 15° away from the next screen angle. The moiré is not usually visible because the Y is so pale compared with the screen that it is interfering with. In your case:
C=67.5
M=7.5
Y=22.5
K=37.5

Y is only 15° from K which should also help hide the visibility of the K/Y moiré.

So the idea is that since White is lighter than Y that should help hide the W/K moiré if W is set to the same angle as Y. And because Y and W are such light colors any interference between Y and W caused by them running at the same angle should be pretty invisible. You're basically doing dot on dot printing of Y and W. So W goes down first in ink sequence.

Michael Jahn at Compose USA can possibly proof this for you as a proofing demo. He's at:

michaelejahn @ composeusa (dot) com

Their inkjet halftone proofing solution for flexo using white and on foils is outstanding.

Attached is a micro photo of one of their flexo inkjet proofs on clear material with halftoned white. (The image detail is the stem of an apple). Click on the image to enlarge.

best, gordon p
 

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Bloodsaler

Well-known member
You print on silver substrate,is there any problem of drying?
The ink on this kind of stock is hard to dry~
 

michaelejahn

Well-known member
You print on silver substrate,is there any problem of drying?
The ink on this kind of stock is hard to dry~

While my experience is only with EPSON white ink from the WT7900 - on both clear and metallic - yes, we have to either wait a moment (before we can run it through the X-rite i1 (eye-one) iSys) - sinve we shrink wrap out software with dongles, i have a heat gun which shortens that down to a few seconds.

Back to the screen angle issue - Bill, if you want to discover if you might have a morie issue before you go on press, you might think about what we discussed before - ripping to TIFF and using Star Proof to drive the EPSON WT7900 - this will show you what you are going to get IMHO ( the H stands for Hairless in my case ).

But, as Gordo points out, no matter what you do, there are only 4 options of 45 degree angles across 180 degrees - so it is either use wo that don't touch so much, or use that 'different line screen' trick.

Hope that helps !
 
Normally, I would send 1-bit tiffs to our vendor for a proof (they can proof white on silver with the EPSON), but I had very limited time on the job so here is what I did -
I chose to put the white on the black angle ONLY because there was very minimal black in the area of the white screen.

I ran the CMYK at 150 lpi and the white at 133 lpi. The product is on press now, and there is no evidence of a pattern whatsoever. Even in the few areas where there is a significant amount of CMYK, there is no problem at all.
Great success! Thanks for all the input.
 

nsk

New member
White screen angle

White screen angle

I think the wholw sequence to be modified.
C=7.5
M=67.5
Y=82.5
K=37.5
W=82.5
You are using the angle of yellow for white
 

Luc St-Pierre

Well-known member
My worries would be more for the linescreen. What linescreen are you printing your white at? For a white ink to cover properly a silver substrate, anilox-linescreen corelation is a key issue. We normally use a 300 anilox with a cell volume of 6.28 to achieve a good white. This involves the white linescreen has to be 85 lpi with a minimum 4% dot on plate. If you print the other colors at another linescreen than 85, you will face more issues than a simple angle set fix-up. Yellow angle would be my pick. If you work with an analog plate, a good old color key will do the job. If you are using laser plates, ask your plate supplier to proof your final color plate files on a single acetate and proof the white plate negative. Put on top of each other, it will do the job also. Hope this helps.
 

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