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Thin Is In

(August 2012) posted on Tue Aug 21, 2012

The role of thread diameter on a variety of printing characteristics

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By Art Dobie

As depicted in Figure 3, mesh with larger diameter thread size is more likely to leave a rougher surface topography on printed ink film compared to mesh with thinner thread diameter. Ink shear (and viscosity drop) ceases once the ink is cut by the squeegee into the mesh apertures. While the printed ink begins its recovery back to rest viscosity, any bigger imprints left by larger filament sizes may not flow out completely, remaining in the ink profile.

Influence of thread diameter on stencil quality
The taller weave of mesh with larger diameter and lower open area can also affect several important characteristics of the stencil coating. The taller profile of mesh having larger thread diameter makes it more difficult to maintain a smooth stencil profile (lower Rz value) when coating with direct emulsion. As the wet emulsion layer dries into the mesh, the resulting surface topography of the coating is greatly influenced by the mesh profile underneath. The dried profile of the stencil coating takes on that of the mesh which supports it from below.

Figure 4 shows two stainless-steel screen types, one with 25-micron wire diameter and the other having a wire diameter of 16 microns. The top set of photos show the emulsion stencil topography on both mesh types when the direct emulsion stencil thickness is just 7 microns. The lower set of photos contained in Figure 4 show the identical two mesh types when the EOM (emulsion over mesh) is increased to 18 microns. The mesh profile underneath influences the coating surface profile particularly when the coating EOM is thin, but is more apparent when the mesh is thicker as a result of larger diameter size.

As diameter increases and open area becomes more closed, the wire weave displays a taller profile. When wire diameter decreases, open area increases and the weave profile is lower and smoother. Because stainless-steel mesh is shiny and reflective, the lower weave profile of mesh having smaller wire diameter and increased open area can in many instances be more advantageous when screen imaging.


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