Successful Emulsion Coating

Coating Screens for Consistent Results
We visit many shops each year to evaluate stencil issues and to shed some light on the various processes involved in making screens. Larger shops often have automatic coaters while smaller shops perform hand coating.
First the auto coaters: Auto Coaters are predictable when set up correctly. By predictable I mean their EOM (percentage of emulsion over mesh) is more consistent. No matter who uses the machine it will consistently apply emulsion the same every time. The key is dialing in coater pressure and speed to achieve the desired EOM.
I have gone into shops where they are coating 3 times on the squeegee side and 2 times on the print side and the EOM is close to 0% because the coater pressure is too high. Coating Pressure, Speed, and the type of emulsion used need to be balanced to achieve the desired EOM. When changing to a new emulsion the EOM should be measured on a test screen and pressure and speed adjusted to meet the target EOM percentage.
  • More Pressure or More Speed equals lower EOM percentages, or less emulsion on the mesh.
  • Less Pressure or Less Speed increases EOM.

Auto Coaters can be programmed with different coating recipes. While a 305 may utilize a 1:2 coat with a sharp edged coater, a 60 mesh may need slower coating speeds, and may provide better results with a 2:3 coat using the dull edge. It all depends on the mesh, the coater settings, and the flow qualities of the emulsion. Generally three to four recipes are all that is needed for textiles, and for UV graphics only one or two is needed since mesh counts are usually in the 300-380 range.

Strong EOM Image

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