The Basics of Screen Printing
What usually comes to people’s minds when they think about screen printing is an old-fashioned t-shirt printer or possible a set up that produces simple posters.
Over the years, technology has become more advanced, and screen printing is now an engineering process that is controllable, measurable, and consistent. Techniques have been developed to contribute to the development and production in advanced manufacturing.
Here are the basic items required for the process of screen printing:
Stencil is media produced by the patterned application of pigment to a surface with the use of an intermediate object with designed gaps that allow the pattern or image to be successfully created. Although stencil is usually referred as the finished product (image or pattern), it is actually both the resulting image and the intermediate object themselves. Stencil can either mean both depending on the context it is in.
This is a flexible polyurethane blade held in a rigid mount or handle. It causes the ink to flow into the mesh and removes excess ink from the top of the stencil.
This can take the form of a wide range of solids or dyes suspended in a fluid. A large range of ink chemistries are available to suit a range of applications.
Substrate is a general term for the surface used which will be printed on. Its surfaces can range from bread to bio-medical sensors or more widely used – paper.
A screen printing press provides the surface for the substrate to be printed, and the upper section secures the screen. It allows movement between the substrate and the screen.
Ink Substrate Relationship
A temporary bond is formed through the relationship of the surface energy of the substrate and the surface tension of the ink. The ink basically wets the substrate.
As the squeegee moves away, the tension in the mesh pulls the stencil away from the ink film. The temporary bond as mentioned before will draw ink out of the mesh openings and leave a film of ink on the substrate. There will always be a small percentage of ink left in the mesh. What removes the ink that is left on top of the stencil is the squeegee.
Basic Screen Printing Machine
Temporary Bond Caused by Adhesive Forces
Images courtesy of PDS International
The processes mentioned above only show screen printing in a much simplified form. The need to have dimensional control of all aspects of the process to within a few microns takes them into the area of high precision engineering.
Here are just some of the technologies that would not have been possible without screen printing:
Flat screen televisions
Special effects graphics printing
For a printing process with such a long history and an evolving future, it will continue to expand its applications for businesses and individuals.