Everything You Ever Wanted to Know About Screen Printing, but Were Afraid to Ask
The Screen Printing Process
Custom silk screen printing was invented by the ancient Song Dynasty of China, but became a common printing methodology with the advent of photography. In 1910, photo-reactive chemicals were first used to bind emulsions to silk screens, allowing silk screen templates to be created quickly, accurately, and affordably.
The process is little changed since then, though the materials have changed significantly. While many use the phrase “silk screen printing” that is almost never accurate anymore. Screens have been made almost exclusively of polyester for decades. The emulsions have also been upgraded to be less toxic and more environmentally friendly. Inks have improved, as well.
As materials have improved, more options are available to custom screen printers. Thread count is an important consideration for screen printers. The thread count of the mesh screens typically range from 40 to 390. Say, for example, you have a 180 thread count screen. Each square inch of the screen has 180 vertical threads and 180 horizontal threads. That creates 32,400 small “windows” between the threads. The ink is pushed through these small “windows.” Lower thread count has fewer, larger “windows” per square inch. This allows more ink to penetrate for better coverage. Higher thread count creates crisper, more detailed images. A gooey, glue-like substance, called an emulsion is applied evenly over the screen. The stencil is “burned” onto the screen by blocking off parts of the screen in the negative image of the design to be printed. In other words, the open spaces are where the ink will appear on the final screen print are the only thing not blocked off. The stencil is “burned” onto the screen, using an ultra-violet light to set and cure the emulsion. The screen is then washed off, removing the emulsion where the UV light did not cure it. The screen has now become a stencil, through which ink can be pressed onto the material only where desired. Each color gets its own stencil. The ink for each color is spread evenly across one end of the screen mesh designed specifically for that color. The mesh is lowered to just above the surface of the material you are printing on. And there are lots of choices there, as well. While people normally associate screen printing with t-shirts, in truth, it is incredibly versatile and can be used for a wide variety of purposes on a wide array of materials, including most fabrics, and papers, polyesters like Mylar, polycarbonates like Lexan, vinyl, acrylics, and dozens of other synthetics. Using consistent pressure, the printer draws the ink across the stencil with a squeegee, pushing the screen onto the material and forcing small amounts of ink through the “windows.” Different types of inks are used depending on the purpose and the material you are printing on. The ink is dried. Some inks are dried using heated, blown air, and others are through UV exposure. The process is repeated for each color.
The Printers’ National Environmental Assistance Center says it “is arguably the most versatile of all printing processes.” It’s true. Here are just a fraction of the things that can be done with this methodology:
- Screen Printed Custom T-Shirts and Other Apparel
- Screen Printed Labels, Overlays, and Stickers
- Both Interior and Exterior Screen Printed Signs
- Screen Printed Banners and Tradeshow Displays
- Screen Printed Fabrics Such as Canopies, Tents, Umbrellas, Towels, etc.
- Screen Printed Bags and Totes
- Collectibles Such as Keychains, License Plates, Souvenirs, Pens, Tchotchkes, etc.
- Screen Printed Electronics Accessories Such as Mouse Pads, Cell Phone Covers, USB, etc.
- Logo Imprinted Asset Labels and Inventory Stickers
Advantages of Screen Printing
- Coverage – Screen printing provides the most complete coverage of your material. It doesn’t create the pixilation sometimes seen in digital printing.
- Cost – There are costs associated with the creation of each screen. Once a screen is created, however, it can be used thousands of times at minimum cost. That makes screen very cost effective, especially for larger runs.
- Color – Screen printing creates the most vivid colors. Also, your screen printer can custom match colors, and is not limited to Pantone or CMYK color charts, the way many other custom printing methodologies are.
- Style – Screening just has the bold, classic look that so many people have grown to know and love.
Disadvantages of Screen Printing
- Color Subtleties – While this methodology does create the most vivid colors, it cannot create color gradient and fades possible with digitally printed labels. Photo quality images are not possible with this methodology.
- Fine Detail – Extraordinarily fine detail cannot be accurately created using this methodology.
- Serialization –Serialized labels are not possible with screen printing. There are many other options for creating serialized data.
- Ruggedness – Screen printing is actually surprisingly durable, but does not withstnad the elements or abuse the way some other methodologies do. There are special UV inks that hold up to UV light exceptionally well, and special laminates can protect these labels from harsh elements. However, compared to laser etched or engraved metal labels, and especially to metalphoto anodized aluminum nameplates, screen printed labels cannot match the year after year endurance.
- Size – This methodology usually maxes out at about 30” x 30,” with many printers stopping much smaller than that. Large format printing may be necessary for bigger projects.
- Speed – Projects involving many colors may be faster on digital printers. Also, custom roll labels can be created using flexography or hot stamping much faster than anything that can be done with screen printing.