What is Screen Printing and How Does it Work?
Screen Printing is a method of printing based on stenciling. It can be used to print on most surfaces, including paper, plastic, fabric, and wood. A fine mesh (originally silk) is stretched across a wooden frame to form the screen. An impermeable stencil (either paper or a photosensitized coating) is applied to it, so that the ink passes through to the area beneath only where an image is required. Once the stencil is attached, the screen is placed on top of fabric. Printing ink or dye is then drawn across, transferring the design to the fabric. A series of screens can be used to add successive layers of color to the design.
How are T-Shirts Printed?
1. At the top of the stack we see the Film. This is a film positive, which is clear with the exception of the image to be printed which is opaque. (black) There are other methods, like painting directly onto the silk with a “hold-out” solution, but typically we use a film, or vellum printed from a computer.
2. Next, a photo-sensitive material called “photo mask” or “photo stencil”, which behaves much like photo film, is exposed to strong light using the film positive as a mask. In this process the light-exposed areas of the photo-sensitive “gel” emulsion becomes hardened. The emulsion areas of the stencil which are protected by the opaque areas of the film remain unexposed and thus soft. In the “development” stage of the process, the exposed areas of the stencil remain hardened, while the unexposed areas of the stencil soften and get washed away, forming the image areas where the inks will pass through.
3. The “photo stencil” is embedded (either before or after exposure) into fabric stretched very tightly across the printing frame. After the stencil dries, the “Screen Frame” is pressed against the substrate (a shirt in this scenario) and ink poured onto the surface of screen is dragged across the design using a squeegee. This results in ink deposited on the shirt. And that’s how screen printing works.