Adventures In Photopolymers With Ben Krasnow

There is a technology that will allow you to add inks, resins, and paints to any flat surface. Screen printing has been around since forever, and although most of the tutorials and guides out there will tell you how to screen print onto t-shirts, [Ben Krasnow] had the idea of putting patterns of paint on acrylic, metal, or even ITO glass for electroluminescent displays. With screen printing, the devil is in the details, but lucky enough for all of us, [Ben] figured everything out and is sharing his knowledge with us.

The ten thousand foot view of screen printing is simple enough — put some ink on a screen that has some photoemulsion, and squeegee it through onto a t-shirt. While this isn’t wrong, there’s a lot of technique, and things will go wrong if this is your first time doing it. Screens are easy, and the best way to get those is by buying a pre-stretched frame. The photoemulsion is a bit different. The old way of applying a photoemulsion is by squeegeeing it on with a bizarre tool. It’s almost impossible to get a thin consistent layer with this technique, so [Ben] recommends just buying some photoemulsion film.

Once the photoemulsion is on the screen and dry, you need to put an image on this. The photoemulsion cures hard with UV, so the traditional technique is using transparency (actually, the real old-school way is using a camera obscura…). Transparency sheets for laser printers work, but 30-lb vellum is actually more transparent to UV light than clear acetate sheets. This is then applied print side down to the dry screen, and believe me when I say this is the most important part. You will not get a good screen print if there is not direct contact between your photomask and your photoemulsion. This is so important, it may be worth considering some experiments in vinyl cutting to create the photomask.

With the screen developed, it’s simply a matter of globbing on some ink and pressing it onto a piece of acrylic. [Ben] used regular oil paints, an unmixed artists’ oil paint, and the professional solution, epoxy-based screenprinting paint. By far, the epoxy paint gave the best finish, but it’s a stinky mess that is nearly impossible to clean.

With a somewhat successful screenprinting setup, what will [Ben] be able to do? Well, he’s been working on electroluminescent displays, and the first EL displays were screenprinted anyway. More than that, you could use screen printing to create a resist for copper etching for creating your own PCBs. There’s a lot you can do when you can put epoxy down in a thin layer, like make a blockchain of Tide pods, and this is the best tutorial we’ve ever seen on using photoemulsions.

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Screen Printing Electroluminescent T-Shirts From Tron

Travel around to enough security conferences, faires, and festivals, and you’ll see some crazy wearable electronics. Most of them blink, and most of them use LEDs. Electroluminescent panels are used for wearables, but that’s a niche – the panels are a little expensive, and you have to deal with high frequency AC instead of the much simpler, ‘plug in a LiPo here’ circuit LED-based wearables have to contend with.

Still, electroluminescent panels are cool, and thanks to how EL panels are made, you can screen print EL displays. That’s what some of the guys at AMBRO Manufacturing did recently: screen printing electroluminescent lights directly onto garments. It’s t-shirts from Tron made real.

EL panels and EL wire are really only three separate parts: a conductor of some sort, a phosphor, and another conductor. Pass a high-frequency AC current through the conductors, and the phosphor lights up. With EL wire, it’s a thick copper wire clad in phosphor and wrapped in a very fine copper wire. EL displays are made with conductive ITO-coated glass or plastic. It’s a relatively simple construction, and one that is perfectly suited for screen printing. In fact, one of the first EL displays – the DSKY, the user interface for the Apollo Guidance Computer – used screen printed seven-segment EL displays.

The folks at AMBRO only have a proof of concept right now, but it is a completely screen printed electroluminescent design on fabric. To light it up, the t-shirt will need an inverter, but this is the beginnings of t-shirts from Tron.

Video below.

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