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.
“You will not get a good screen print if there is not direct contact between your photomask and your photoemulsion.”
IIRC the offset shop that printed our local newspaper half a century ago used a vacuum frame to hold the negative onto the photosensitive aluminum printing plate. Building a successful vacuum frame should easily be within the reach of any of us. The UV exposure was done, IIRC, with a carbon arc, also a piece of technology within easy reach. Avoid letting anybody look at the arc, or at any other high-powered UV source.
The place where I worked and learned the art also used a vacuum light table. It’s a great method, but for hobby use I’ve found the glass plate works nicely. And if you’re just doing some hipster design on a t-shirt, you can be pretty sloppy. I’ve never had any trouble with a scoop coater – until it’s time to take the emulsion off and you have a thick drip at the edge of the image area. Those can be hard to remove. I wish he’d gone into exposure tests, but other than that, fantastic video.
We always used a regular shop light to expose our screens. The key to slikscreen printing is the Zen in the process of coating and printing by hand. Spend about 2 hours inside printing posters and you’ll be so “zened” out on the fumes and then the entire process just seems to happen. “Man the stars are birght tonight! Wait, why are they under the clouds!?” said me.
Use pantyhose to cover the screen. Apply photoemulsion with a putty knife. Lift pantyhose ccarefully off of screen. Hang screen with a slight tilt. Since most of the photoemulsion stuck to the pantyhose, you’re pretty much left with a very thin layer that just needs to drip in one direction tto smooth itself out.
EPROM eraser UV lights may work. Or even a scanner. See how many passes are required.
The whole process got me interested when he rolled out the premade films. Now we’re talking.
“squeegeeing it on with a bizarre tool” It’s called a scoop coater. The frame with stretched screen is mounted vertically in a bench vise. The scoop coater is like a mini rain gutter, as long as the width of the screen. Hold the coater against the screen and tip just until the emulsion flows out to touch the screen. Smoothly lift the coater up the screen to the top.
Put the screen in a dark room to dry. A second coat can ensure there are no pinholes and make the bottom side of the screen smoother. Smoother emulsion = less edge fuzz from exposure light leaking into dips around the edges of dark areas of the artwork.
The easiest way to ensure best contact between the screen and artwork is to build a box that fits into the frame, and place a piece of UV transparent glass on top of the artwork to mash it down onto the screen.
For printing, do what’s called “off contact”. Space the frame so the bottom of the screen sits about 1/16″ to 1/8″ above what you’re printing onto. When the squeegee is dragged across the screen, it gets pushed onto the substrate then pulls back up so ink can’t wick between the screen and substrate.
Automated machines that are super rigid can have off contact distance set on the screen clamp or by adjusting platen height. For simple manual setups with hinged frames it’s easiest to attach spacers to the bottom of the frame corners.
If you’re the sort of person who plans on building a multi-station screen printing machine, here’s something I read in Printwear Magazine back in the 80’s. Long enough ago that any patents should be expired. A press company was working on a large machine using chains to move the platens. They struggled with the inaccuracy of commercially available roller chain. So they had some super precision and very expensive chain made. It worked great, for a while. Any small amount of wear and the accuracy was no better than normal chain.
Then one of their people hit on an idea. Instead of relying on the chain to do the positioning, they could use inexpensive, sloppy chain and mount interlocking, tapered guides on the platens and frames. That way when each frame came down it’d grab the platen and force it into precise registration. they could make huge oval presses with as many stations as desired, and have zero problems with holding registration.
That’s one of the main things with any kind of multi-station screen printing, aligning the colors to one another. Without the capability of having every platen and screen in perfect alignment to one another, your art people have to be able to make designs that will look good with color separations that vary quite a bit in registration. Not good if you need to do CMYK full color work.