What is Screen Printing?
Screen printing is a process though which ink is mechanically applied to a substrate via the use of a screen and
squeegee. In it's basic form, screen printing is a very simple process. First we start with the artwork. Each color of
the design requires an individual screen so we must separate the design into its component colors. This is done on
the computer and each color separation is printed to a transparent sheet.
Next we must prepare the screens. The screen is a rigid frame of wood or aluminum that has a fine mono filament
nylon mesh stretched over it. This mesh is then coated with a light sensitive emulsion that will become the stencil
through which the ink will pass when printed. The screen is then mounted, with the separation, in an exposure unit.
This machine exposes the screen to high intensity UV light.
Exposing the Screen
When the UV light hits the emulsion a chemical reaction hardens the emulsion making it water and solvent resistant.
The separation acts as a shield to block the light in certain areas of the screen. These soft areas are then rinsed
away with water to create the open area of the stencil.
The screens are then mounted in the press and registered, or aligned, so that each color prints in the proper location
relative to the other colors. Ink is loaded into the screens and squeegees are installed. The actual printing is
accomplished by pushing ink through the screen and onto the shirt with the squeegees. As the squeegee scrapes
across the screen it fills the stencil with ink while simultaneously bending the mesh down to transfer the ink to the shirt.
To create the composite image on the shirt, individual colors are printed then the shirt is moved to the next color.
After test prints are run to check alignment, shirts are loaded one by one and printed. Once all the colors have
been applied to the shirt it is removed from the press. The ink on the shirts is still "wet" at
this point and needs to be "dried".
The ink we use for t-shirts is the variety called "Plastisol" and is not actually "dried" but cured with heat. Plastisol is
made up of polyvinyl chloride resins (PVC), plasticizer and pigments. When plastisol ink is heated the PVC resin
particles swell and absorb the liquid plasticizer and these swelled particles merge with each other and form a solid
film. Curing of plastisol ink is accomplished by rapidly bringing the ink up to curing temperature ( ~330° F ) with
electric or gas infrared heaters.
To cure the shirts we run them through a "drier" that utilizes a conveyor belt to pass the shirts under infrared heating
panels. The shirts spend between 30 seconds to 1 minute in the dryer, and when they come off the belt they are
done and ready to be folded and packed.
Step 1 ( create the stencil )
Step 2 ( prepare positive film )
Step 3 ( burn the image on the stencil )
Step 4 ( wash the image out )
Step 5 ( dry the stencil )
And that the silk screen stencil is Done!
Can start printing now.