Proven advice for industrial applications and other situations where delivering less-than-flawless prints isn’t an option.
By Mike Young
Without getting overly involved with mesh comparisons, consider two similar grades separated only by a 3-micron difference in thread diameter. One leading brand’s 355/34 plain weave polyester (meaning 355 threads per inch with a thread diameter of 34 microns) has a physical opening of 29 microns that provides an overall open area of 16 percent. (See Figure 3.) This means that only 16 percent of the ink can be transferred onto the substrate’s surface to create the image. The reason for the restriction is interference from the threads and crossover knuckles, which collectively consume 84 percent of the fabric. That’s good for sieving and filtration, but not for critical screen applications. If the ink contains large particulates – as many in functional applications do, such as conductive pastes and phosphor (for electroluminescence) – then the fabric’s petite openings may negatively affect coverage and/or image detail by impeding the ink transfer.
The second grade is a 355/31 mesh, with a 31-micron thread. Just this one difference vastly improves both the mesh opening size and percentage of open area to 38 microns and 28 percent, respectively, as shown in the lower half of Figure 3. Mesh interference is reduced by more than 14 percent, while particulate size becomes less of an issue. Many are loathe to venture down this avenue, however, believing it can affect the overall deposit thickness and/or opacity, and this could happen. After all, the second mesh is thinner (48 microns compared to 54).
But the key word is could. In actuality, the thicker mesh with its higher peaks and deeper valleys creates long, narrow tunnels from which the ink can have difficulty “excavating” itself, promoting pinholes and streaks. (See Figure 4.) With the 355/31 mesh, the ink layer may be a little thinner, but the ensuing gains can be exceptional and may reduce the reject rate. Quality soars: The squeegee pressure is reduced, creating less distortion; opacity and uniformity of the ink deposit are superior; less dot gain/loss occurs; and colors are truer, to name but a few of the advantages.
Secret #3: Control the Tension
Did you enjoy this article? Click here to subscribe to the magazine.