pre-press and mark andy 2200 help

[alexinessex]

hi wonder if anyone can help please.
have a friend who is in need and my area of pre-press and press is limited to sheet fed litho so a little lost on the following.

they have a: Mark Andy 2200 Flexographic, lines on rollers range 200-800 , depth 10-25, 6 stations.

pre-press wise the rip they use is: Agfa Avantra 30 running with an Agfa Apogee PDF rip and run negative films and make: Ace Nyloflex plates.

they want to find the best settings to run 4colour print - so my questions are:

1. what is the maximum screen they can run on the mark andy?
we run 200 screen on our B1 speedmaster but cant find the info for a flexo machine

2. can anyone suggest the best dpi to output films once the screen is determined?
all our images are 300dpi and gives us great results. again no idea for flexo

many kind thanks all in advance

 

[Bartman43072]

Re: pre-press and mark andy 2200 help

The general rule in flexo for determining halftone lpi is "1/4 the anilox cell count", so theoretically, you can run a 100 lpi screen on a 400 lpi anilox (screened roller), this doesn't always hold 100% true, but it's a good general guideline. The volume (depth) of the cells on a given anilox also comes into play. I have customers that run Mark Andy 2200's using a 187 lpi screen on 660 - 800 lpi anilox rolls (this is achieved on BASF NyloFlex ART, a slightly softer material than ACE).

The important part of screening for this kind of flexography is the highlight dot. You can't just fade a screen to nothing like you can in most offset applications. With flexo (or any relief plate) dots below a certain size will drop off the plate during the washout, so you need to make sure that the minimum dot size on your film is big enough to hold on the plate (typically 1-2% minimum). ACE should hold a 1% dot at 150 lpi, however during plate exposure, the dot will grow to a 3-4%, and on press it will gain to about 10%. This is just about the most challenging aspect of flexo printing. Various prepress provider have a number of different schemes for reproducing dots that fade to white (vignettes) including minimum screens with dot removal (quantum), or hybrid screening where the conventional (AM) dot transitions to a Stochastic (FM) dot and then scatters to produce the vignette effect. I use EskoArtwork's Hybrid screening in a variety of different applications with tons of great success, but your talking about a fairly substantial expense to get set up for that.

The other thing to consider is cutback. Narrow Web Flexo (like on a MA2200) typically generates a 15-18% dot gain at 50%, so when outputting films you have to find a way to cutback your screens about 15% (50% cut to 35%). Again, we use EskoArtwork's FlexoCal, works great, costs a fair amount. I have not had experience with the Apogee RIP, but it probably has this capability.

We run all our films at 2400 dpi on an Avantra 44, 300 ppi for images should be plenty, lower is OK for lower LPI.

Hope this helps a little!

-Bartman