is a Dual Cure a Photopolymer + Diazo?

[kidink]

Can anyone tell me if adding diazo to a photopolymer is essentially creating a dual cure emulsion or are they completely different? in the same way can you use a dual cure without any diazo as a photopolymer?

Will adding diazo to a photopolymer mean that it's pointless post exposing?

Are dual cures superior to photopoylmers for resolution/halftone/details?

For a shop that prints a lot of discharge and uses an LED exposure unit are there any benefits to a photopoylmer or a photopolymer+diazo over a dual cure.

[BP]

Here is the best interview that breaks all of it down.

https://www.youtube.com/watch?v=mMJqQgQQlzU&t=43s

[kidink]

Great video thanks for posting, a lot to digest but super informative.

I'd like to talk more about the pros and cons of a Dual Cure v Hybrid Photopolymer with diazo added (Triple cure)

To clarify, can diazo be added to a SBQ Photopolymer that doesnt have a UV Photopolymer in it's chemsirty?

[RICK STEFANICK]

The Diazo will help if you running water base inks and with resolution. Straight up photo polymer has no water resistance. Remember when you do this your exposure times will increase dramatically.

[ABuffington]

Adding diazo to a pure photopolymer does not make it a dual cure.  Like Rick says it aids in adding water resistance and better resolution.  Diazo emulsion is just pure diazo, no SBQ (sensitizer for pure photopolymers).  A dual cure is part SBQ emulsion as well as diazo emulsion and sensitizer.

Pure Photopolymer Emulsion - Fast Exposures - Add diazo and it increases time since diazo exposes slower.  Excellent mesh bridging, durable, more EOM typically.  1 year shelf life without diazo - 4-6 weeks optimum performance once diazo is added.  Exposes well on all exposure systems.

Dual Cure Emulsion - Wide latitude of exposure, slower exposure than Pure Photopolymers - Diazo must be added for optimum performance.  Combines the qualities of SBQ and diazo.  It uses different PVA's and Vinyl Acetates.  Good mesh bridging, good halftones.  These emulsions can be fine tuned for either solvent resistance or water resistance by the manufacturer.  4-6 week shelf life once diazo is added.  DOES NOT expose properly on LED.  You can get an image, but the SBQ portion is exposed and hardens before the diazo can get exposed, compromises edge quality.  Exposes best on Metal Halide or Graphic Fluo tube systems.

Diazo - Slower exposures.  Exposure needs to be complete for durability.  Good resolution.  4-6 week shelf life once diazo is added.  Economical.  Exposes well on all exposure systems.

Emulsion choice has many variables.  Ink resistance is number one, followed by desired resolution, durability on press, what exposure unit you use.  EOM?  This is a key area for quality printing.  Zero EOM causes early breakdown, poor edge quality, dot gain and saw toothed line work. 

Found a sensitivity chart on what wavelengths the different types of emulsions are sensitive to.  This is an over looked area in most screen rooms.  You can have a light emitting 405nm when the emulsion exposes best on 365nm.  It will still image, but resolution and on press durability can be compromised.  Metal Halide lamps are often fine tuned for the emulsion used. (light spectrum tweaked for diazo sensitivity, same for pure photopolymers, or all of the emulsion types).  Multi Spectral Metal Halide bulbs are best at exposing all emulsions types.  LED is fine as well.  Newer emulsions like our T9 are tuned specifically for the 405nm wavelength that LED typically uses.  However a high wattage Multi Spectral Metal Halide will create more cross linking of the sensitizer and emulsion.  LED exposure of a pure photopolymer like T9 gets even better when the screen is post exposed since LED doesn't cross link completely as much as a 5k-8k metal halide muti spectral lamp. 

[kidink]

Thanks I appreciate the input, interesting that dual cures are not recommended using an LED unit, I’ve never heard that before and a lot of sales reps have never mentioned it.
Alan for a shop that does a lot of discharge printing and also a lot of high detail sim process work and uses a I-Image DTS and LED exposure unit what would you recommend?

[markdhl]

Olite Metal Halide exposure light in lieu of the LED light would help you a lot with your set up. Alan knows all about the olec lights ..

Mark Diehl
Douthitt
313 515 8635

[Dottonedan]

Thanks I appreciate the input, interesting that dual cures are not recommended using an LED unit, I’ve never heard that before and a lot of sales reps have never mentioned it.
Alan for a shop that does a lot of discharge printing and also a lot of high detail sim process work and uses a I-Image DTS and LED exposure unit what would you recommend?

Pretty much what Abuffington said.

We had an I-Image STEll and we printed a lot of discharge using dual cure emulsion. At the time of my leaving, we were near 1 discharge base job a day probably. That was a lot for us. The kicker is as they say,  The LED was not strong enough to build a strong durable screen (for water base) printing, but for most, that would be if you want to be safe at all times for large and small runs.

The reason we could use it, was because the orders we did, were discharge base only, and smaller quantities. Our screens would last our entire order. The suggestions are all based off of preparing everyone for the worst case scenario such as “needing it to last for the longest time possible, like for 10-50,000 unit orders. Like If you want to do an order for 10,000 shirt using water base and discharge, then use dual cure emulsion with a stronger light source.  For many, it works just fine or was "good enough”.   There’s that term again.  Then you have the question of (Are you trying to also hold the small dots of 3% in a 65lpi on a 305 mesh with discharge waterbase).  If so, again, you may want to use the the stronger light to penetrate long and strong.The LED can expose dual cure halftones well, 45-55lpi pretty good and the cure and stencil (for us) was strong enough for lower quantities.... but as you get down to the small dots of a 3% in a 65lpi on 305 mesh coated 1:1, the dual cure, requires too long of an exposure to keep the benefits of a fast LED and you can’t hold them as easily because they are too fine of a dot for that long of a time that dual cure requires and are over exposed in those areas.  That’s what I’ve seen anyways. When we wanted to hold small detail, even though the order was short, (50-500 shirts) we would run with the stronger exposure unit.  If it were solid art or big halftones, (we never used big dots) but if it were solid, we could run LED on dual cure no prob. Again, it wouldn’t last for long runs, but 95% of ours were well under 500 units.  I think on larger orders, they would also burn two sets of screens for any water base as a back up. I don’t think we used them much if ever, but they were there.

I don’t remember the emulsion brand. Wasn’t my area. Kinda had a rubbery feel to it. I feel like it was Chroma-line.

I think the M&R LED unit wavelength is right near or at 380 from what I remember seeing posted here some time way back by Rich Hoffman. It was at that, but not over I think it’s how it went.

[RICK STEFANICK]

THE BOTTOM LINE IS:
1) Yes, You are going to get superior resolution with dual cure's. But remember youR resolution is only as good as your film, files OR the quality of your DTS and light source.
    so you can be using the best emulsion( there are 2100 opinions on what that is here on the forum) but not make screens as good as the guy using a cheap photopolymer if
    if your out put, art quality and light source are not in line.
2) Why would you want to use a duel cure with out the Diazo when there are so many excellent photo-polymers available.
3) A dual cure with the right light source,exposure time and hardner will give you a superior water resistant screen. Period