screen-print

Screen-printing forces ink or emulsion through a fine mesh screen onto a substrate: fabric, paper, plastic, wood, or metal. The screen has areas blocked by hardened photographic emulsion or hand-cut stencil, so ink passes only where the mesh remains open. A squeegee blade pushes the ink across the screen with controlled pressure, depositing a layer typically 10 to 25 micrometers thick. The result is a flat, opaque print with crisp edges and uniform color density.

The mesh counts between 40 and 380 threads per inch, chosen based on ink viscosity and desired detail. Coarser meshes (40-110 TPI) accept thicker inks and deposit heavy layers for textiles and industrial coatings. Fine meshes (200-380 TPI) hold thin inks for detailed graphics and electronics work. Fabric screens are woven from polyester, nylon, or stainless steel monofilament. The substrate sits on a squeegee arm or pallet below the screen, which is held in a frame and can be manually or mechanically lowered onto the work.

Photographic preparation and ink chemistry

A photographic screen begins with a blank mesh coated in light-sensitive emulsion. A film positive (film with opaque image and transparent surrounds) is placed against the coated screen and exposed to UV light. The exposed emulsion hardens; the unexposed parts under the film positive wash away, leaving holes in the emulsion where ink will print. This photographic method allows production of fine detail and precise registration. Alternative methods include hand-cut lacquer or paper stencils, faster but cruder. Screen-printing inks are typically plastisol (polyvinyl chloride in plasticizer), water-based acrylic, or solvent-based formulations. Plastisol requires heat curing; water-based dries by evaporation and suits fabric with minimal setup; solvent-based offers fast cure and works on numerous hard substrates but requires ventilation.

Common problems include ink bleeding under the screen edge, caused by improper squeegee angle or excessive pressure, and emulsion breakdown from insufficient exposure time or overexposure to solvents during cleanup. Off-contact printing (slight gap between screen and substrate when stationary) reduces bleeding and extends screen life by limiting ink squeeze at the edges. Registration marks ensure multiple color passes align correctly. Exact positioning of the substrate on the pallet and consistent squeegee pressure are critical for uniform output.

Screen-printing dominates apparel decoration, producing millions of graphic t-shirts annually, and is standard in electronics manufacture for applying solder paste to circuit boards and conductive coatings to glass. Industrial uses include decorating ceramics, signage, and product marking. The process tolerates coarse surfaces and thick deposits better than offset or flexography, making it suited to textured substrates. For production runs under 1000 pieces per design, screen-printing remains cheaper than digital alternatives. The setup time and per-unit cost drop significantly once the photographic screen is made, making it economical for moderate volumes and simple designs.