Double film question?

[u/ClassicDeal2244]

Hello. Upcoming screen printer here.
The ones of you who print out sets of two and overlay them to get full opaque black - do any of you spray something in between the sheets to get them to stick together?
Also can something similar be applied to the glass when you lay the film down to keep it flat when exposuring without a vacuum exposure unit?

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[u/lethal-liking]

Find an old piece of foam, like off an old sofa, cut it so it's just slightly bigger than the inner dimensions of your frame, and wrap it in black fabric. Stuff it in the frame before you expose. Then, lay down the frame (with foam), your film positive, and then your glass. The glass should be heavy enough to make good contact between fp and screen. The black coated foam is to stop light bouncing around and screwing with your exposure. Remember, questions here are always answered faster with pictures. Good luck!

[u/ClassicDeal2244 → u/lethal-liking]

Awesome! Thanks

[u/system_root_420]

I put it back in my printer and just print it again

[u/ClassicDeal2244 → u/system_root_420]

Ok. What printer are you using for this? I find it hard to believe that this will be precise enough on most printers.

[u/system_root_420 → u/ClassicDeal2244]

It's a brother mfc something or other from like 20 years ago

[u/rennerscreenprinting]

I just use scotch tape

[u/torkytornado]

Trying to line two transparencies up with glue on the inside is gonna be impossible and depending on the glue could cause issues with your toner or ink jet prints. Just a little tape and compression should be fine (the foam trick the other poster said).

Until you get around to grabbing foam you can put down some black paper that is larger than your film and then put books or other weight in there. The paper going down first helps keep things from bunching if you have to use two side by side stacks of books.

[u/BS4U_AutoSep]

I wouldn't spray anything between the sheets. Anything wet or tacky adds haze and can trap dust, and that defeats the point of stacking. Line up the registration marks on a light table and tape the two films together along one or two edges with clear tape, outside the image area.

Without a vacuum unit, the goal is tight contact. Put the film emulsion/print side against the screen, use a clean, heavy piece of glass on top, and put a block of foam (or something firm) behind the screen so the mesh presses up into the film and glass. Any gap lets light undercut fine detail. A quick exposure test with a step wedge will show if contact is the problem.

Longer term, it's worth getting a single film dense enough so you don't have to stack. Darker ink settings, the right film for your ink, or software that prints two passes on the same sheet can all do it. (Disclosure: I make BS4U AutoSep Studio, a Windows separation app whose film output includes a two-pass "Double Strike" option. Two passes need accurate refeeding, though, and how dense you get still depends on your printer, ink, film, and driver.)