Screen Angles - No more left

[RichB]

Hi,

I have a flexo job which is cmyk white and Pantone 300. All tone work is interacting.

We have put P.300, white and black on same angle and had a wet proof made and it looks good, but it is in perfect register.

Printer is not happy as he thinks that when job hits the press and mis- registers (0.2mm tolerance) that he will get screen clash.

Does anyone think the printer has a point or is he been over cautious. I don't want it to be an expensive lesson to learn!!

 

[PantherMac]

Without seeing the artwork, it's impossible to tell, however I've been in similar situations before. You have to look at the actual area's where the screens interact, to determine if there's really going to be a problem. It's usually a case of the PMS color trapping into the process work? You can evaluate the trap area, and decide if moiré in that sliver will cause a problem (I've seen it...). This usually gives you some direction on the angle(s) to choose. Alternatively, you can use a different line screen ruling for your '5th' color (or whatever one isn't 'fitting' w/ the rest - again, usually the PMS).
Is the white ink screened at all? If it's just a solid under-printing color, it's angle is irrelevant, so you can ignore it. Otherwise, I would look to print it (and possibly the PMS, again, depending on the work) at an alternate line ruling. This should eliminate any screening errors, but ask your printer what LPI's to use (as their rollers can make all the difference).

- Mac

 

[Luc St-Pierre]

I would suspect that the areas containing PMS 300 will not have cyan values into it. In that case PMS and cyan on the same angle should work. I have once put the PMS (which was a green) on a straight 45 degree to print clean edges. This applied in a situation where no magenta (that I output at 38 degree) interacted with the green and all anilox rolls were at 60 degrees.

 

[David_Modprint]

Perhaps Seek Advice from Printer

Perhaps Seek Advice from Printer

I would suggest you ask the printer for their advice, they must have run into this situation before. I also suggest as others stated, analyze the areas of conflict and adjust your angles based on that interaction. Otherwise, again, without seeing the actual artwork, perhaps I might suggest using an FM screen of some type if the problem area is not critical.

 

[RichB]

Thanks for the replies.

Just to clarify all 6 colours have tone work interacting. We've managed to retouch all black out of scan and replaced with the P.300. So only issue left is the white.

Does anyone think using a stochastic screen for the white would work?

We've also requested films from the printer with the white on the same angle as the P.300 and will try to mis register films and see how far we can push them without getting unacceptable screenclash.

 

[David_Modprint]

What color stock is this printing on? That might make a difference in the solutions.
Like I suggested, try using a stochastic screen for white, if it's the least most noticeable color,
otherwise perhaps use it on yellow. I use it for yellow almost every day.

David

 

[kyle]

Are you supplying film/plates to the printer? Can you just give them the files and let them handle it? Or does "printer" mean "pressman?" Maybe tha'ts a UK vs. US thing.

I wonder wether FM screens are often used in flexo, given the nature of the process. If FM is okay, I agree with David_Modprint: make the white and yellow FM, perhaps with a larger than normal dot size if FM is problematic for flexo (I'm assuming you'd need to make two inks FM, since you have six and you wrote that all interact).

If you need to stick with conventional screening, you can treat Pantone 300 as an additional process color, then you can max out the black generation and use only two angles for the hue inks (cyan, magenta, yellow and Pantone 300) because aside from black and white, you would only have cyan + Pantone 300, Pantone 300 + magenta, magenta + yellow or yellow + cyan. The cyan and magenta could both be 15 degrees, and the Pantone 300 and yellow could both be 75 degrees. This leaves 45 degrees for your black and 0 degrees for the white, or vice-versa depending on which is stronger. Pantone 300 should then be printed before magenta, cyan and black in the ink sequence to preserve the transparent interactions with the normal process inks. You can send me a sample of the artwork containing an area where all inks interact, and I'll send you back an example.

Barring FM screening and using Pantone 300 as a process ink, and assuming you have interacting screens (not just solids) between every possible ink pair, your options would be:

Identify the two process+spot pairs that have the least interaction and make the spot angle the same as the process angle, risking the moire.

Make the yellow and white different screen frequencies at two different angles that would each be the same as another ink, which may not eliminate moire and could make it worse, depending upon how close the ratio of the frequencies is to a simple harmonic ratio. I usually attempt to preview moire by printing a small area in question from the 2400 ppi plate image to a 600ppi inkjet at 400% size.

Convert the image of two inks to line art, rendering tints as coarse alternations, similar to wood cuts or the old AT&T logo. This can be done semi-automatically with Photoshop.

 

[meddington]

Is the white ink screened at all? If it's just a solid under-printing color, it's angle is irrelevant, so you can ignore it.

I'm having a hard time envisioning where white ink would be screened with process and spot...and still be pleasing to look at. As stated prior, seeing the artwork would help.

 

[RichB]

We have to supply print ready digital artwork and in this case the printer will not go to press unless we advise him on how output this area. Obviously this means we would be liable for any press down time/new plates needed.

The wet proof done already (a true flexo machine proof) with P.300 and White on the same angles looked great, but was in perfect register.

The stock is clear film which will be wrapped around an aerosol can. I have attached a cropped psd of the area that is difficult.

If you can imagine the P.300 fades into a picture and the underpinning white of the picture fades out. Therefore alot of the problems will be hidden by the can shine coming through - hopefully!!.

I have retouched the black out so the scan is now only cmy P.300 and white. P.300 and White would have to be on same angle.

Its the first time in 20 years I've not managed to retouch image to ensure all necessary areas do not interact - bit of a bxxxh/challenge.

However, advice of white on a stochastic screen gives us another option to try if the printer has this screening capability. Original option of white and 300 on same angle as long as when label mis-registers it doesn't twist too much still looks a possibility too now there are only 2 inks which will share the same angle. So thanks and I'll let you know if it was successful.

Have a great New year to all
Rich

 

[DavidMa]

Do you have the option of running the white as a different line screen?
We run a screen set here that has the black and yellow on the same angle, but have different line screens and it works great.