An investigation of the effects of image angle on resolution of fine detail screen printing

Screen printing, unlike other printing processes, requires ink to be pushed through the image carrier to the substrate. When the mesh threads and their intersections cross the image area, they act as obstructions to the ink flow. In large image areas, the effect of mesh interference is minimal. In fine detail screen printing, mesh interference is a primary cause of poor or inaccurate resolution. The trend in screen printing has been toward more and finer fine line, halftone and four-color process printing. Researching methods to minimize mesh interference will enable screen printers to gain greater control over the printing process and better utilize technologies currently available for fine detail reproduction. Previous experiments had shown that the angle of a fine line image relative to the mesh threads will have an effect on resolution quality. This thesis developed a theoretical model for hypothesizing that image angle may also affect resolution in halftone screen printing. A fine line test image was developed to attempt to reproduce the results of experiments indicating a critical angle exists for fine lines, and to determine if the direction of the squeegee motion is also a factor. Halftone gray scales screened at all of the common four-color and black and white reproduction angles, as well as at the aforementioned hypothesized fine line critical angle, were used to determine if image angle has an effect on reproduceable tonal range and on the accuracy of resolution in halftone screen printing. Exposure and squeegee conditions were optimized, and the test images were printed. Data on fine line and halftone resolution was collected and statistically analyzed to determine if image angle had an effect on the resolution. In all cases, angle was found to have an effect on image resolution. However, no one angle or small range of angles was found to provide significantly better resolution than another. In the fine line test, it appeared that a relationship does exist between image resolution and the direction of squeegee motion. This was not evident in the halftone resolution data. The halftone data, however, does indicate a relationship exists between loss of percent dot area and tonal range. Further investigation of these factors in screen printing is recommended