In screen printing, the wet printing process is used to apply graphics to flat and cylindrical surfaces. It has a low cost and can be used on various materials including fabric, paper, glass, ceramics, plastic, and metal.
Screen printing is not only used to apply ink; any material with suitable uniformity can also be printed. For example, solder paste is screen-printed onto circuit boards during the soldering process, decorative film panels are printed using screen printing frames, and even butter can be screen-printed onto sandwich bread during mass production. Most types of ink are suitable, which means this method can print graphics on almost any surface.
All screen printing techniques use the same simple process. It is suitable for both manual and mechanized operation systems, and the print quality is equivalent.
The screen printing process consists of three steps
A charge of ink is deposited onto the screen, and a rubber squeegee is used to spread the ink evenly across the screen. Those areas protected by the impermeable film Istencill are not printed.
The screens are made up of a frame, over which a light mesh is stretched. The mesh is typically made up of nylon, polyester or stainless steel.
Each colour requires a separate screen. A full-scale positive image of each colour is printed onto a separate sheet of acetate. The areas to be printed with ink are black and the areas not to be printed are clear. The full-scale positive is mounted and registered on the screen, which is coated with photosensitive emulsion. The emulsion is exposed to ultraviolet light, which causes it to harden and form an impermeable film. The areas that were not exposed, under the black parts of the acetate, are washed away to produce the stencil.
There are 4 main types of ink: water- based, solvent-based, polyvinyl chloride- (PVC-) based plastisol, and UV curing. Water and solvent-based inks are air-dried or heated to accelerate the process. PVC-based plastisol inks are used mainly to print textiles. They have varying levels of flexibility, determined by the quantity of plastisol, which can cope with stretching fabrics. They polymerize, or harden, when heat is applied. UV inks contain chemical initiators, which cause polymerization when exposed to UV light. These inks have superior colour and clarity, but are also the most expensive.
Screen printing is utilized in various industries due to its ability to print on a wide range of basic materials and its cost-effectiveness. Typical products include plastic items, wallpaper, posters, flyers, banknotes, clothing advertisements, artwork, and packaging.
Ink can be directly screen-printed onto the surface of a product or onto a label that adheres to the surface. Screen-printed graphics are applied to film panels used for decoration in the production of consumer electronics and similar products.
Scratch-resistant ink is employed for direct mail, mobile phone top-up cards, and security applications, applied through the screen printing process.
Printed circuit boards (PCBs), radio frequency identification (RFID) chips, and other electronic applications are typically created by coating surfaces with copper and then selectively removing it to produce electronic circuits. However, nowadays, electronic circuits can also be screen-printed using conductive ink. Flexible materials can be printed in this manner, and transparent conductive inks are even available.
Screen printing produces graphics with clean edges. The inks have a paint-like consistency and so will not run or bleed in most cases.
The definition of detail and thickness of printed ink is determined by the size of mesh used in the screen. Heavier gauges will deposit more ink, but have lower resolution of detail. These tend to be used in the textile industry, which requires copious amounts of ink, whereas light meshes are used to print on paper and other less absorbent materials.
Almost any material can be screen printed, including paper, plastic, metal, ceramic and glass.
The costs for equipment are typically low, but they depend on the number of colors as each color requires a separate screen.
Mechanized production methods are the fastest and can print up to 30 products per minute.
Labor costs can be high for manual techniques, especially for complex and multi-color jobs. Mechanized systems can operate for extended periods without intervention.
Ink for printing on bright surfaces typically has less environmental impact. Inks based on PVC, formaldehyde, and solvents containing harmful chemicals can be recycled to prevent water pollution.
Screen printing is an efficient use of ink; applying ink directly to the product’s surface reduces material consumption.
Screens can be recycled by dissolving the water-resistant stencil layer from the mesh for reuse.