Most people only know
screen printing by the end result: an image on a t shirt. What they don't know is the process of getting that image onto the shirt, or even the fact that it's not just for shirts. With the right
inks most any surface can be printed on, even wood, metal, and glass. For this post we'll keep it simple though. Just how did your favorite
t shirt come to be?
First we start with the artwork. Before you print anything you have to have the art ready. The best case scenario is to have the art in a high resolution, digital format like a Corel Draw, Adobe Illustrator or Photoshop file. With simpler, single color designs sometimes all you need is a 300dpi jpg. If none of these are an option you can work with the
graphic designer at the shop to recreate your art or create custom art from scratch.
Once the artwork is ready it's printed onto transparent sheets and becomes a
film positive. If your design has more than one color a separate film positive is made for each color.
This is where the
screen part of screen printing comes in. These mesh screens will be coated with a light sensitive material called
emulsion. Once dry the film positives are ready to be
shot or
burned into the emulsion.
To burn a screen we use a high intensity UV light in a vacuum sealed light table. The light hardens the emulsion except for the areas blocked by the film positive. These areas remain soft and wash out easily creating something similar to a stencil.
Once the screen is washed out a negative of the original image is left over. Ink can now flow through the image area while the hardened emulsion blocks the rest of the screen.
Screens are then set up on the press to be printed. For multi-color designs each screen is carefully
registered with the others. This insures that the various colors print correctly together without overlapping or leaving gaps between them. The shirt is then placed on a
platen covered with a small amount of adhesive to make sure it doesn't slip out of place. On a manual press screens are lowered on top of the shirt and squeegees are uses to push ink through the screen mesh and onto the garment.
For larger orders an automatic press is used. On this type of press the shirts are lifted into place and the squeegee is machine operated. All the printer has to do is register the screens, set printing options, and load the shirts.
Once a shirt has been completed it is removed from the platen and placed on a conveyor dryer. The dryer heats the wet ink up to
cure it. Typical screen printing inks won't dry until they hit a certain temperature. Once they do the ink is set and the shirt is ready to wear.
