Mar 20, 2018
Here’s an overview of screen printing basics, the auto screen printing version. If you’re looking for a manual edition of the basics of screen printing, we wrote that a few years back. The easiest way to think of screen printing is as a photographic stencil process. First, we print film positive, which we will use later to create the stencil on the screen. Next, we prepare a screen with light-sensitive emulsion and line those films up on the screen. We then expose that screen to light and develop it, which creates a stencil where the film covered the emulsion. After that, we push ink through the stencil and onto a garment. The result is a fancy new t-shirt for you. Want more juicy details about screen printing basics? Good, we got ‘em. Read on!
At Offbeat Press, we specialize in high quality, professional screen printing. Despite this process being a common method, most people are unaware of the steps involved in creating screen-printed shirts. In the following article, we’re going to give you a run-down of the entire process. Whether you know everything there is about screen printing basics or you’re completely new to the process, there’s a little something for everyone here.
The logo you designed, the idea you had while joking with your friends, the design you made for a specific event–this is where it all begins. 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, whether we create it or we are provided with a pen and ink piece to scan and prepare. For some specifics on how to prepare artwork, please visit our art guidelines.
Quality artwork is essential for quality screen printing. There are many ways to create artwork for screen printing and different benefits from different separation processes. We won’t get into the complicated details of simulated process or 4-color process right now, but we will definitely have articles on those in the coming future.
The simple steps of separating artwork begin by sizing the design to print size. “Print size” literally just means the size you want the image to be on the final garment. Vector artwork is best, as raster art can sometimes look “fuzzy” around the edges, depending on the quality of the original file. Speaking of things being fuzzy, if you’re still fuzzy on our art guidelines, please check out the link above. We can’t stress this enough. If the original art is poor quality, the print will be poor quality, unless it is recreated in a high-quality format.
At print size, we paste the file into a registration template and trim each color in the artwork so that no colors overlap. After we separate and group the colors together, we swatch specific Pantone colors for each group. Then, we add information pertaining to the job, such as the customer name, job name, and ink colors. From there, we print the file onto waterproof transparency or, as we call it, “film.” Each color prints out solid black, which will assist in creating the stencil we mentioned earlier.
The transparency film used to expose screens. Each color gets its own piece of film.
Most supply companies make screens with a wood or metal frame. Monofilament polyester mesh is stretched over the frame and glued in place to create a high-tension surface. Wood frames tend to warp over time, they don’t usually lay level on press and they lose tension quickly. In short, you should only use wood frames for DIY projects at home. We only use aluminum metal frames to ensure reliable screen tension, perfect color registration, and the best possible quality prints.
Screens were originally made with actual silk, hence the term silk screen or the National Serigraphic Society’s term, serigraphy (Latin for “silk” and “to write or draw”), but the industry has since moved on to the polyester we use today.
Screens are available in a variety of mesh counts and sizes, with different screen sizes working with different presses. Mesh count is determined by the number of threads per square inch. Low mesh works best with specialty inks (such as shimmer or metallics) and large areas of low detail, both of which require a large amount of ink to pass through the screen and onto the shirt. In contrast, high mesh screens allow for less ink to pass through but result in the ability to print incredibly fine details.
A clean screen, ready for emulsion.
We begin by reclaiming a screen, ensuring it is free of all old emulsion, residual ink, belly button lint, or other debris. Any residue or chemicals leftover in the screen from its prior use can have a negative impact on the quality of the impending print.
Once we clean and dry the screen, we apply a precise number of coats of light-sensitive photo emulsion. That precise number of coats can change, depending on the mesh. There are dozens of different emulsions, each with their advantages, disadvantages, and different coating techniques.
Although this may seem like a simple step of the process of screen printing basics, it is one of the most important. If done incorrectly, problems can snowball and become larger issues down the line. Many shops struggle with this step and end up using “band-aids” once the order is on press to fix these mistakes. We pride ourselves on being a step above the rest, especially when it comes to our pre-press knowledge.
The final step in the coating process is to dry the screens so they’re ready to expose. Once dry, we’re ready to use those films we printed earlier to expose the screen and create our stencil.
Screens coated with emulsion, ready to expose.
Now that we have our artwork printed on films and screens 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. There are dozens of different screen meshes, each serving a slightly different purpose in achieving a high quality print. Typically a rule to follow is: the higher the detail, the higher the mesh count. Of course there are always anomalies, but we won’t bore you with those details this time around.
In our shop, we have two main steps in the exposure process: artwork registration and screen exposure. We start by aligning all the transparency films perfectly on our pre-press setup registration unit. We use a magnifying loupe to ensure perfect registration before we adhere each film to a carrier sheet. By aligning the artwork before we burn the screens, we can ensure that all films will work together perfectly and, most importantly, we can save time spent on press setup.
Transparency film placed on carrier sheets and ready to expose.
Screens on the exposure unit, ready to burn.
The exposure unit is a powerful light source used to expose the screen for a varying period of time, depending on the type of emulsion, coating technique and screen mesh.
We engage the exposure unit and hundreds of LED lights expose all of the emulsion not covered by the film positive. The lights cross-link any emulsion molecules unprotected by the film, thus hardening them. Any emulsion molecules covered by the film remain water-soluble.
Exposing a screen.
Once exposure is complete, we develop the screen, which is a fancy way of saying we spray out the screen with water in our washout booth. The “soft,” water-soluble areas that were covered by the film in the exposure unit wash out within a couple minutes, leaving a stencil of open area that we will later push ink through. Now, we can finally start setting up the job to print! Notice I didn’t say we can start printing yet. There’s still work to be done, but if you’re not a screen printing nerd like us and have made it this far, hang in there. We’re almost to the printing stage.
Developing a screen.
The next step in the screen printing basics process is, as stated above, more work. Without getting into too many secrets, different screens require different pampering before they’re ready for press. After exposure is complete and the screen is fully dry, we then put the screen on a light table to check for artwork accuracy and pinholes. Once we take care of any and all pinholes, we tape the edges of the screen frame to keep ink from getting into the edges and sneaking through onto the substrate.
If you’ve perfected every step in the artwork separation and pre-press process, you’re finally ready to print! While you can make some adjustments on press, bad screens will be magnified once shirts get on press. The press setup can be quick and painless if the registration was spot on in the pre-press department. Placing the screens in the press in a specific, predetermined order, we use a specific on-press set-up tool which perfectly registers our screens to one another. That’s just a fancy way of saying this tool lines the colors up to one another perfectly.
Our inks are all coded using the industry-standard Pantone Matching System. We use Pantone Uncoated colors from the Solid Uncoated color book for all water-based inks because those are most accurate to the natural tones of water-based inks. We use Pantone Coated colors from the Solid Coated color book for the synthetic plastisol (petroleum-based) inks because they are more accurate to those color tones. Choosing ink colors in screen printing is a science, especially when working with water-based inks. Please check out our Ink Colors page for more info and our stock colors.
Once we have our screens dialed in for perfect registration, it’s time to select our squeegees and floodbars, load the ink in the screens and print some tests.
We use the floodbar to fill the stencil in the screen with ink. When we print a shirt, the floodbar moves forward to fill the stencil gasket and then the squeegee drops down to make contact with the screen and shear the gasket of ink onto your shirt. Similar to the variety we see in screen mesh, different squeegee firmness (durometer), types and widths are available to suit different screen printing needs. Different durometers have different strengths when it comes to screen printing and can drastically influence the details of your screen printed t-shirts.
We’re in the home stretch! We lock the screens into the correct order, choose the proper squeegees and floodbars and lock them into the proper print heads, we load the respective ink colors into each screen, and now we print a test. In terms of the entire screen printing basics process, this is where the rubber meets the road, as it were. The print carriage moves forward and the floodbar fills the stencil gasket with ink. Once the print carriage reaches the end of its flood stroke, the floodbar disengages as the squeegee engages, making contact with the screen. The print stroke continues and the squeegee shears the ink through the stencil onto the test shirt. We perform this same task for every color in a design. From this test shirt, we confirm proper registration, print location and artwork accuracy before we start printing your order.
Running the first test of the white screen.
With the test completed and everything perfect, we print the first actual shirt from the order. For this example, we printed a 2-color water-based design. The first color printed is gray. Once the first color prints, the pallets index (rotate around the press) and thus, the shirt moves around the press to the next print station.
The first color printed on our black shirt.
If this was plastisol, we would need to flash this print before we printed the next color. A flash is essentially just a mini oven that goes into one of the print stations instead of a screen. “Flashing” the print just means heating up the ink to the point where it gels into a semi-solid state. Depending on the ink, that could mean 150 degrees F or 220 degrees F. Once plastisol gels, it is dry to the touch. We can then print the next color on top of it without smearing the image at all.
Since we are screen printing water-based ink, flashing the first color isn’t absolutely necessary. Water-based inks have much different properties than plastisol inks. For this example, we won’t be flashing the gray ink. The press indexes until the shirt moves into the print station containing the white screen. Once the pallets lock into place, we print the white screen. The press indexes once more, moving the shirt into the unloading station. The printing is done!
Our two-color shirt (white + light grey), printed and ready to cure.
We cure shirts by laying them on a conveyor belt that is full of heating panels. We send the shirts through at specific speeds, based on the type of ink printed on the shirt. As the shirts move through the chamber, the dryer forces 320 degree air through the print, removing any moisture from water-based prints and completely solidifying plastisol prints. Some specialty inks require specialty temperatures, so we adjust the dryer settings for those situations. How do we know we’re hitting the right temperature? Read on!
Our completed shirt, passing through the dryer unit to cure the print.
All throughout this whole screen printing basics process, we’re checking and double-checking every step to ensure accuracy, which includes final cure temperatures. We use an infrared temperature gun to confirm shirts are reaching the perfect cure temperature. Beyond the use of this tool, we also perform wash tests, stretch tests, twist tests, and other tests inspired by Chubby Checker to be certain our work will be on your chest for years to come.
Using our temperature gun to ensure the ink is reaching curing temperature.
Of course, there are hundreds of variables and details that change with every order, but this summary covers the general screen printing basics. We hope you learned something new or enjoyed brushing up on what you already knew. Questions? Comments? Get in touch with us directly here.