Screen printing involves securing a mesh screen to a frame and blocking the mesh openings in non-patterned areas, allowing the printing paste to pass through the open mesh and transfer onto the fabric. Screen printing evolved from the stencil printing process. Screens were originally made of silk or phosphor bronze wire but have largely been replaced by screens made of synthetic filament fibers. The mesh size is selected based on specific process requirements. Patterns are typically created using a photosensitive process: the mesh is stretched taut and fixed to a frame, then coated with a photosensitive emulsion (such as polyvinyl alcohol or gelatin mixed with ammonium dichromate). After drying, a transparent film bearing the design is placed over the screen for exposure to light. Finally, the screen is washed with warm water to remove the unexposed emulsion and then reinforced, resulting in the finished printing screen.
Screen printing involves the preparation of the printing screen itself. (Historically, screens were made of fine silk-hence the term "silk-screen printing"-and although silk is no longer used, the name persists in the industry.) The screen consists of a fine-mesh fabric-made of nylon, polyester, or metal wire-stretched tightly over a wooden or metal frame. An opaque, non-porous film is applied to the screen fabric. The opaque film is removed from the areas corresponding to the design, leaving behind the open mesh; this area is where the pattern will be printed. In most commercial applications, the screen fabric is first coated with a photosensitive film, and the pattern is revealed by removing the film in the design areas through a light-exposure process. To print, the screen is placed over the fabric. Printing paste is poured into the frame, and a squeegee (a tool similar to a car windshield wiper) is used to force the paste through the mesh openings.
Each color in the design requires a separate screen to allow for the printing of distinct colors. For example, a three-color print requires three screens to apply the three colors to the fabric. Furthermore, the pattern elements for each color must be precisely aligned on the screens to ensure accurate placement after printing-preventing errors such as the green stem of a rose being printed across the middle of its red petals. "Registration" is the industrial term for the accurate alignment of all pattern colors during printing.
There are three primary methods of screen printing, all based on the same fundamental principles. The first is manual screen printing; widely used in the 1920s, it remains in use today for small-batch, high-fashion garments or prototype products. The second is automatic screen printing-also known as flat-screen printing-which features an automated process and relatively high production speeds (approximately 500 yards per hour), making it suitable for fabrics like terry cloth or for small-batch, intricate printing. The third method is rotary screen printing, a continuous process that offers the fastest production speed (exceeding 3,500 yards per hour) and is currently the most widely used screen printing technique [3-4]. However, a major drawback of screen printing is its high water consumption and the generation of significant amounts of wastewater during production.