screen printing > Screen Making

cap films vs. indirect films vs. direct emulsion

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StuJohnston:
I have tried to read all of the threads that may have information about this topic. Unfortunately, the most detailed explanation that I have found is that cap film is better for detail than direct emulsion. I have also read elsewhere that you can stack cap film for a thicker stencil. From what I have read here and elsewhere is that indirect films are on their way out.

Here is my take on the subject. I have only used direct emulsion so far, so I can't compare the methods side by side, but I can give my experiences with emulsion. I have not had any problems with detail when using  direct emulsion. I have yet to try this, but Kiwo claims that it's poly plus HWR can achieve an 88lpi stencil! Maybe that's low compared to cap film, I don't know. I just got phantasm cs for illustrator and I will try to test this out with the halftone function. My main issue with cap film is expense, I haven't quite settled on an emulsion so it's hard to tell exactly how much I am spending per screen, but I am certain that it doesn't compare to the price of cap film.  After looking a little further into this, it looks like the best I could hope for with WB inks is, 'some water resistance.'

When I got my vac frame, it was made to be part of a platemaking system. Which meant that it wouldn't accomodate a screen frame. For a moment I considered indirect film because I could just toss that into the vac frame without a second thought then apply to screen. Then I read up on it and found out the truth of the matter. IT looked like it would cost me roughly $10 per screen and the process to get the stencil to the mesh seems more complicated than even direct emulsion. A big issue was that it wouldn't do waterbased either. I have since started to turn the platemaker into a frame suitable for holding a screen frame so I am not as interested in indirect film, but still curious.

What I would like to know is what you guys think about the various methods of making stencils. I feel like there must be something to cap film that I don't see, so I am open to suggestion. I mainly use air dry, mild solvent inks, so lack of WB capability wouldn't be the end of the world.

A related issue is the comparison of methods of sensitizing in direct emulsion. I have some qx-1 that claims to be dual cure, yet it lasts a year and exposes in about 10% of the time that my Kiwo poly plus dual cure emulsions do. Which leads me to believe that it is actually photopolymer. Am I wrong or is ulano trying to pull a fast one?

I just had a brain flash, why not put some unprinted sticker material on each container to add up the screens per coating session! Thankfully I have quart containers that I empty the gallons into so I should be able to start fresh on ounces per screen and then cost per screen.

Frog:
First off, figure cost all you want, but be assured that micron for micron, cap film is more expensive. It is, after all, essentially emulsion made in a convenient shape, and you are paying for that convenience and eom consistency.

As for your dual cure, yes, it's a photopolymer with diazo as well.

StuJohnston:

--- Quote from: Frog on September 12, 2011, 11:59:01 AM ---First off, figure cost all you want, but be assured that micron for micron, cap film is more expensive. It is, after all, essentially emulsion made in a convenient shape, and you are paying for that convenience and eom consistency.

As for your dual cure, yes, it's a photopolymer with diazo as well.

--- End quote ---

I just find it strange that the qx-1 basically behaves like a pure photopolymer. At least to the best of my understanding.

I was thinking that one of the major advantages to cap film is that it is much less susceptible to user error. Thankfully, I am the only person in the shop and therefore the main screen coater and I am confident that I am getting consistent results. I may see if I can get some samples later on, but for now I am pretty happy with my current set up.

I just thought of another question. As you mention, one of the advantages of cap film is that the EOM can be determined pretty well by the thickness of the film. Does the cap film come through to the squeegee side? Does this effect the Rz value? For that matter, does Rz matter on the squeegee side?

jsheridan:
The only thing we use cap film for anymore is High Density and a few specialty inks. The stuff is stupid expensive on a per screen rate and not any easier to apply than direct.

You can adjust your EOM with coating techniques and different solids content emulsion to achieve any thickness you desire these days.

ZooCity:
Oh boy Stu, I think I have some answers to your queries.  We've used both cap film and direct emulsion in the past.  We still use cap film in a pinch.  I don't care what anybody tells you, cap film is the fastest way to get from reclaim to stencil ready to shoot. 

Murakami Aquasol HV is our direct.  Ulano EZ-Film (roughly 45micron I believe) and Chromaline Magnacure 38micron are our cap films.  The Aquasol and EZ are pure photopolmer, the Chroma is a dual cure. 


--- Quote ---Unfortunately, the most detailed explanation that I have found is that cap film is better for detail than direct emulsion.
--- End quote ---

It can be.  The main reason is that cap film is retarded perfect (when applied correctly) across the entire stencil area.  Even with excellent coating technique and proper face coating it is difficult to duplicate this when coating by hand.  That said, you can get really close using direct emulsion with skill.   It's this consistency and then the amazing RZ value (smoothness) on the print side that give cap film a leg-up on fine detail.  Cap film yields what I would call a "theoretically perfect" stencil in that the maximum amount of EOM is on the print side and the print side surface has the lowest possible RZ value.  This combo can provide most excellent detail.
However....


--- Quote ---Does the cap film come through to the squeegee side? Does this effect the Rz value? For that matter, does Rz matter on the squeegee side?
--- End quote ---

It inherently has to just a little in order to grab onto the mesh and stay there through resolution and then on-press for entire print run.  While having just the minimum emulsion on the squeegee side and the max on the print side is beneficial to holding detail on the stencil, when it's time to actually print it generates friction on the squeegee blade which creates chatter (which then gives you an un-even print), uneccesary wear on the mesh, increased pigment staining and added wear on your printer or your machine. 

Now, there are two methods for applying capillary film.  The more common is to either roll it on or, using a backer board, draw it up into a wetted screen.  This method is fast and can be executed with wet screens, immediately after reclaim but it will exacerbate the above problems.  The other method involves degreasing and drying the "blank" screen as you normally would for direct emulsion coating and then applying the cap film by "printing" a bead of copacetic emulsion onto the screen and adhering the film that way.  This method, presumably, would put some EOM up on the squeegee side and eliminate the above issue to some degree.  I wouldn't know though because at this point you're not getting much advantage out of using cap over direct so I don't incorporate the technique.

My favorite stencils are ones consistently coated with direct emulsion and then face coated on both sides.  While a cap film stencil may be technically capable of holding more detail at exposure, this direct emulsion screen is going to excel on-press.  RZ on the squeegee side does make a difference.  If you want to feel/see how much, try the face coating method above using an emulsion formulated for low-RZ like Kiwo Poly Plus Z. 


--- Quote ---why not put some unprinted sticker material on each container to add up the screens per coating session!
--- End quote ---

I've done this and while Andy is right on the money when he says that cap costs more "micron for micron", I've found that Ulano's EZ-Film is cheaper than our average cost per direct coated screen.

You had a bunch o' questions and to sum up my thoughts on stencils generally, I'm in the "one emulsion for them all, coat it all direct" camp these days and I do have employees to wrangle.  My main reasons for this are for the flexibility you get out of direct and the fact that we will be printing a lot of wb/discharge.  However, the right shop will see a huge advantage in going with cap film, especially a cost-effective one like the EZ. 

This argument, just like the shur-loc panels v. bolt mesh one boils down to this- who would you like to pay to do the labor of coating your emulsion? 


--- Quote ---A related issue is the comparison of methods of sensitizing in direct emulsion. I have some qx-1 that claims to be dual cure, yet it lasts a year and exposes in about 10% of the time that my Kiwo poly plus dual cure emulsions do. Which leads me to believe that it is actually photopolymer. Am I wrong or is ulano trying to pull a fast one?
--- End quote ---

I surely need someone to qualify this statement but I believe they are all technically "dual cures" with some containing diazo and some omitting it.  If you threw diazo into your QX-1 it would have a shelf life and expose slower. 

Let me know how you like Phantasm CS, I'm very interested in that program but have not had time to give it a good whirl.  Those phantasm software folks appear to be actually considering us printers and, *gasp*, even accommodating us as a trade. Just a tiny little snowflake in hell they seem.   

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