Burining better halftones

[Cole]

I'm having issues achieving good burns on halftones. Before getting into it, here are my specs...

Printer: Epson 7600
Film: Film Direct generic roll
Ink: Film Direct dye black
Program: Photoshop
RIP: Accurip Black Pearl
- Drop Density 12
- Resolution (8 pass) or sometimes the max res (2400)
LPI: 55
Mesh: 180s and 225s
Emulsion: CCI LXP
Coating Method: 1/1 sharp
Exposure unit: CCI LED (8 amps)
Exposure time: still figuring it out. Anywhere between 7-10 seconds. I've been using a 21 step guide, but these 3 second differences don't affect the steps by much.

So what I need advice on is how to get the less opaque areas to burn. The smaller halftones never seem to come out. Not sure what percentage of opacity they are. As far as my step guide is concerned, my burn time is correct. So I start trouble shooting backward from there. I have no way to measure my EOM, so I skipped that, which brought me to my RIP settings. I did some reading on here and saw someone mention that Epson recommends using the highest resolution even though that eliminates your control over drop density. So I tried outputting some halftones that way, but still no luck.

I feel like the light is undercutting my halftones or something. When looking at the film, the dots seem dark enough to print, but when I go to wash out, it takes some serious pressure to get those suckers developed. Realistically, what percentage halftone and what LPI can I expect from an ink and film system? I know that DTS allows for much better halftones and burns. So is 55LPI too high for ink and film? Or am I doing something wrong?

[3Deep]

What color mesh? I've found out over the years that a color mesh is best for burning fine halftones, coating 1/1 with the sharp edge of the coater and using a dual cure emulsion has worked wonders for me.  I soft wash my screens and then I use an old spot remover gun with water in it to get the really small halftones clear.  you might want to drop down to a 45 lpi I use to use 55 but found out that 45 does the trick for most of what we do here even 4cp.

[Atownsend]

You might need to bump up your mesh count to get the really fine dots under 10%. I dont think we usually hold anything under 7% @ 55lpi on 230/40 (basically the same as 225/40). Also running 7600, film direct ink, fixxons film, accurip. Eyeball linearization... so there is that... (anyone want to read my films ??!!). Doesn't sound like your positive is failing, depending on the %s you're trying to expose maybe the screens just need a bit more soaking in a post exposure tank and a bit more patience on washout..... just be consistent and spray the screen evenly so you dont eff yourself.. We tend to use a lot more water washing out halftones. like triple the water, triple the time. Inspect with a 10x loupe. You can also always clip the dot %'s to what you can actually hold on screen, makes things a lot cleaner.

[screenxpress]

I always thought you multiply the lpi times 4.5 to arrive at the screen mesh.  No?

If that is correct, I'd bump up to 305 for 55 lpi.

Or as 3Deep suggested, try outputting at 45 lpi and see if that helps at least on getting the dots to expose.  But I think you'll get better results using 305's.

[Colin]

My gut feeling tells me this emulsion is not designed to be high resolution.

If you add diazo to it - the diazo will act as an anti halation additive - this means you can resolve finer details.  But be prepared for a 20-30 second burn time....

[GaryG]

Colin has a fine point (pun intended)
Pure Photopolymer emulsion is not going to give the detail you seek.

Get a Dual Cure that uses a powder sensitizer. Use your PP emulsion for all other printing.
There are a dozen emulsions within the brands. 

Colored mesh a must and is an anti halation motivation over white mesh

Thanks for the new term - to me Colin - "anti halation additive - regarding emulsions".

[Colin]

No Problem Gary!

I had never heard Diazo explained to me that way until I was talking to Al at Murakami some years ago.  I ran with it.

I started calling Diazo an "anti halation additive" to people I talk to so they understand its nature better.  Printers certainly gravitated to it better with that knowledge!