Davis sheds light on how ink quality and mesh tensioning play a role in eliminating ghosting.
By Rick Davis
Ghost images can be problematic for all screen printers. You can print textiles, plastics, glass, or metal and end up with ghost images. You can run the job on manual or automatic presses and see ghosting. We know ghost images can appear independently of substrate and press selection, but why are some print runs more susceptible to producing distinct ghost images than others? How can you have ghosting after you print a sample run of two dozen but experience none after a 2000-piece job?
We can come up with a good answer by taking into consideration the primary causes of ghosting and what steps we can take to minimize their effects. This month, we'll take a look at how inks and screens influence the occurrence of ghost images on our jobs and discuss some of the simple ways we can keep them at bay.
The effects of inks
We can trace the generation of ghost images to pigment particles from the ink becoming trapped between the knuckles of the mesh—the spot where two threads intersect. A number of ink-related factors determine the degree to which ghost images may appear.
The first aspect to consider is the quality of the inks you use. This may sound crazy at first, but the higher the quality of the ink, the greater the potential for ghosting to occur. Ink manufacture involves grinding pigments and mixing. These pigments pass through a mill that breaks the materials down to a predetermined particle size. The particle size of the pigments in the ink plays the greatest role in the appearance of ghost images. Fine particle sizes allow for a higher pigment load, which can yield rich, dense, and vibrant color in an ink. And even though the actual opacity of an ink is determined by a number of different factors, high-opacity inks are typically designed to have a high concentration of pigments. That attribute almost always contributes to the appearance of ghost images in our screens. So the more pigment you have, the greater the potential for ghosting to occur.
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