Silk screen, also know as screen printing, is a straightforward technique that can be used to print signs. The bright, durable ink may be printed on plastic, wood, paper, glass, metal, cardboard and other surfaces. Screen printing is versatile enough to makes signs large and small.
Choose a sign material from paper, board, wood, metal, plastic or pressed board. What size will your sign or signs be? The end use of the sign will determine the necessary size. Purchase or gather your sign substrate. Screen printing is a good technique for multiple prints.
You will need to put your design on a transparency, also known as a film positive; check your transparency for opacity, as the design must be very opaque to successfully burn a screen. Create a design in a graphics program such as Adobe Illustrator, Photoshop or InDesign. Openoffice Draw is available as a free download. Another option is to create a sign by hand and scan into your graphics software, then scale it to the size desired. Scan at a high resolution if you plan to enlarge the design. For large signs, you may have to output one letter or one word at a time. There are prepress companies that are able to output large film positives, but it is expensive.
Your screen frame should be slightly larger than your signs. Using a piece of heavy board with a straight edge, coat the screen with emulsion on both sides and remove excess. Let dry 12 hours.
To expose the screen, place the film positive on top of it so it reads backwards and tape into place. Put film positive and screen on top of the foam with the positive facing up. The foam should fit inside the screen. Place the glass over the positive, weigh down the edges of the glass with heavy objects such as books. Hang the Halide light above the frame and expose for recommended time. Check emulsion instructions for exposure time position of light source. Develop with warm water spray. The emulsion should wash out of the frame where ink will pass. Blot the screen with newsprint to remove excess emulsion.
Place your sign material on a flat surface. A print table with screen hinges screwed onto it is ideal, but a flat cement floor will do fine. Place the screen over the printing material and put some ink in the screen along the end opposite you. Firmly hold down the screen and pull the ink toward you with a squeegee, forcing it through the screen onto sign material. With large screens, it helps to have another person hold down the frame while you print.
If the design did not print, try two or three pulls on the squeegee, thinning your ink or using a more open screen mesh. If the ink blurs, try exposing a screen on a finer screen mesh. It is helpful to pull your first several prints on cheap paper until the design prints clean.
Screen printing supplies are available at many art supply stores and from screen printing supply companies.
Buy ink prior to screen mesh. Often the ink company will recommend the proper screen mesh count, such as 230 or 305 mesh, for a given ink. Screen mesh will vary widely from 80 mesh to 355 mesh.
It is possible to buy stretched screens, saving the step of stretching the screens yourself.
Try elevating the area below the print surface to help with clean contact between the squeegee and poster material. Pressed board called masonite is ideal for this. Cut a piece of 1/4-inch thick masonite with a margin 1 inch larger than your poster size all around. Place your posters on this surface while printing.
Solvent-based screen printing inks should be used with proper ventilation and possibly with a mask.