Feb 26, 2014
Here at Offbeat Press we specialize in professional, human-powered screen-printing. Despite this process being a common method of printing, many people are unaware of the basics of manual screen printing. Well, we’re here to run you through some of those basics.
Although this is a relatively simple process, to achieve a professional level of quality is by no means easy. There is a lot that can go wrong throughout the entire process, and a lot of details to be mindful of in order to achieve a quality screen printed t-shirt or other garment. Good thing we’re a bunch of nutty, detail-oriented folks here at Offbeat!
The easiest way to think of screen-printing is as a photographic stencil process. Ink passes through a screen that we expose to light to create a stencil. The result is the screen’s image transferred to the print surface and a fancy new t-shirt for you. Want more juicy details? Good, we got em’. Read on!
This is where it all begins. Manufacturers create screens by stretching monofilament polyester mesh over a wood or metal frame to create a high-tension surface. Though printers originally made screens with actual silk, hence the original term Serigraphy (from Latin words “silk” and “to draw”), the industry has since moved on to the polyester we use today.
There are all different sizes of screens and each is available in a variety of mesh counts. Low mesh works best with specialty inks that require a large amount of the ink to pass through the screen and onto the shirt, while high mesh screens allow for less ink to pass through but also result in the ability to print incredibly fine details.
We begin by cleaning a screen, ensuring it is free of all old emulsion, belly lint or other debris. Anything leftover in the screen from its prior use can have a negative impact on the quality of the impending print. We clean and dry the screen, we apply a couple coats of a light-sensitive photo emulsion.
At this point we’re ready to expose the screen and create our stencil. But hey, where does our artwork come from?!
Good question! Artwork can come from a variety of sources, but at the end of the day the final artwork must come from a professional design program. For some specifics on how to prepare artwork, please visit our art guidelines.
Once we have the artwork finalized we do pre-press art separations at print size, creating a different layer for every ink color and turning all colors to black. Then we print each color layer in the design onto transparency film, until we have a black transparency film for every color in the artwork. Off to exposing our screens!
EXPOSING THE SCREEN
Now that we have our artwork and a screen coated with our light sensitive emulsion, we’re ready to move forward exposing, or “burning,” our screens. We need to create one screen for each color in the design we’re printing. We start by fixing our transparency film to the screen and placing it in our exposure unit.
The exposure unit uses a powerful light source to expose the screen for a variable period of time that depends on the artwork detail and screen mesh we’re using. During this time the areas of the transparency film that we printed black will prevent light from reaching the emulsion and therefore allow us to remove those areas easily in the next step. The clear areas of the transparency permit light through to harden the emulsion.
Once exposure is complete we spray out the screen with a power washer in our washout booth. All of the areas where light was not allowed to reach the emulsion will wash away, while the emulsion exposed to the light remains in the screen. Thus, our stencil is born! Let’s make some shirts!
Now hold on just a second there, sparky. Don’t get too excited. We still have work to do before we can print your shirts. Remember that film we used to create our screen? We’re not done with that just yet! We need to use that on-press as a guide for setting up all of the screens used in this design. Remember, we need a separate screen for each color we’re printing, so we have to make sure those screens all line up with each other real well, otherwise known as registration. Spot-on registration is key to a quality screen print.
INKS + SQUEEGEES
Once we have our screens dialed in for perfect registration, it’s time to select the components that will bring this shirt to life, our inks and squeegees.
Our inks are all coded using the industry standard Pantone Matching System, specifically from the Solid Coated color book, to help us and our customers be on the same literal page when it comes to colors for their designs.
We use a squeegee to force the ink through the screen and onto your shirt. Similar to the variety we see in screen mesh counts to suit different printing needs, squeegees are also available in varying levels of firmness, known as durometer. Different durometers have different strengths when it comes to printing and can drastically influence what your printed t-shirts look like.
Huzzah! Your screen printed t-shirts are almost here. We have everything we need and the screens set up and at this point there’s only one thing left to do; print! With our ink loaded on the screen, we pull the squeegee across the image area while evenly applying downward pressure. This forces ink through our screen stencil and onto the shirt resulting in a perfect copy of our image. Well, perfect if you know what you’re good at what you do.
If this is a 1-color design and the ink is darker than the shirt, then this garment is done and we can cure the print. But if the ink is lighter than the shirt, or we have to print two or more different colors on the garment, then we need move this shirt to the flash unit. The arms on our printing press revolve around the unit and lock into place so we can print multiple shirts at a time, even when we’re printing numerous colors without removing the shirts from the boards.
When we flash the print, the ink we already printed dries to the touch, but is not entirely cured or permanent yet. But this flash will allow us to print additional colors, or print the first color a second time to achieve better opacity, all without affecting the ink from the first print. Once we have all colors fully printed, the shirt is done!
We cure the ink by running the shirt through a high temperature, conveyor belt dryer. Inks must reach a specific temperature in order to be cured and become permanent on the shirt. But how do we know we’re hitting that temperature? Final step, go!
Throughout the entire order we’re checking shirts to ensure the ink is fully cured and everything looks like it should. We use an infrared temperature gun to ensure ink temperature reaches its curing point in the dryer chamber. We then use a variety of hands-on tests to be certain our work will be on your chest for years to come.
There are, of course, numerous variables throughout the entire process. But this summary covers the basics of screen-printing, for those not intimately familiar with the process. If you have any other questions, please check out our blog archive for more info on screen-printed t-shirts, or get in touch with us directly here.