Screen printing has been used for centuries and although there have been many improvements with the technology, the process still consists of forcing ink through a stencil covered fabric or wire mesh which has been mounted in a sturdy frame. The ink goes through only the open areas of the stencil and is deposited onto a printing surface positioned below the frame. Screen printing is very versatile and it is often the only printing process capable of handling certain applications.
The equipment costs for screen printing are lower than other printing processes, but the rate of production is usually slower. Manual screen printing can be accomplished with only a few simple items: a sturdy frame, screen fabric, stencils, squeegees, and ink. Automatic press equipment is available which greatly speeds up the process, but it is no match for the output delivered by press equipment used for other print processes.
Screen printing can be performed on almost any type of material including paper, glass, fabric, plastic, wood, and metal. Products as varied as signs, posters, circuit boards, mugs, clothing, and soft drink bottles can be printed using the process. Screen printing is very useful when an image needs to be wrapped around an object or when images need to be printed onto oddly shaped manufactured objects.
|Fabrics for screen printing are selected because of several properties. One type of fabric may be suitable for one application and not another. Fabrics are classified according to the following properties:
Most fabrics used for screens are made from one of the following materials:
|Knife cut stencils are created with manual cutting and can be paper, water soluble, or lacquer soluble.
Photographic stencils are made of photosensitive materials and require the use of film positives for exposure. There are three types of photographic stencils: indirect, direct, and direct/indirect.
There is a wide variety of inks available for use with screen printing. The ink for some applications may need to be resistant to ultra-violet light or they may need to be scratch, fade, or chemical resistant for other applications. Most of the inks for screen printing are applied with a heavy coverage so the ink layer takes a long time to dry. The printed products can be air dried on racks if the number of printed pieces is small, but most often a heat source is used to speed up the drying, especially if the screen printing is performed with higher speed, automatic equipment.
Most large volume screen printing is performed on automatic printing equipment which makes the process much more efficient and cost effective. Manual screen printing is still used for many of the smaller runs or for specialized applications. The basic press types are listed below:
- Flatbed: A flatbed press is used for printing on flat substrates.
- Flatbed Cylinder: A flatbed cylinder press is much like a letterpress flatbed cylinder press and is used for longer runs of flat applications.
- Cylinder: A cylinder press is used for printing on round or oval objects.
- Textile: T-shirts and other clothing items are printed on a textile press.
- Precision Flatbed: One of the major uses for the precision flatbed press is circuit board printing.
- Rotary: Higher production rates are a benefit of the rotary presses. The ink is pumped into the printing cylinder and a squeegee on the inside of the cylinder controls the flow of the ink.