Screen Printing Tip of the Week: Preventing Moiré Patterns

Heads up Screen Printers!!!  Kieth Stevens has a great tip on how to combat Moiré, a technique that even some seasoned printers don't know about (as published in Impressions Magazine): When printing halftones, a radiating pattern sometimes appears. This pattern, called a moiré, occurs when the pattern of the mesh or screen fabric conflicts with the pattern of the halftone line count. Moiré also can be caused by the artwork’s patterns, or the interaction between the patterns and the substrate’s texture. Sometimes, the moiré pattern doesn’t appear until after the artwork is printed. A common method for countering this pattern collision is to increase the mesh thread count by a factor of 4.5 times. For example, if the moiré pattern occurs when using a 55 line halftone count, you would increase the mesh thread count to 230. For the most part, this solution will work; however, using higher mesh counts to eliminate the moiré pattern can result in a white underbase that is less opaque. Another strategy is to custom stretch the screen mesh at an angle that will eliminate or reduce the moiré prior to burning the screen. To do so, stretch the frame, put it on the stretcher and lay a mesh over it. Then, take the positive film that contains the halftone art and lay that down on the mesh as if you were placing it to burn the screen. If you see a moiré pattern appearing between the mesh and the positive, rotate the mesh and leave the film in the position that you want to burn it. As you rotate the mesh, you will see the moiré pattern move and change. Keep rotating it until you see the moiré reduce to almost nothing. Lock down your mesh at this exact angle and leave the film in the proper position for printing. Finally, place the positive back down on the stretched and adhered mesh and you should see that the moiré pattern is gone. Mark down on the mesh the location of the registration so that after you coat the mesh with your emulsion, you can once again place the film on the screen, tape it down and expose the image as you normally would. International Coatings manufactures a complete line of phthalate-compliant screen printing inks, including a wide variety of whites, specialty inks, special effects inks, color matching systems, additives and reducers.  For more information on our products, please visit our website at www.iccink.com.     International Coatings:     The Intelligent Choice