Direct Emulsion Troubleshooting Checklist


Direct Emulsion Troubleshooting Checklist



















































































































































































































Problem Possible Cause Solution
Poor definition (edge sharpness) or "sawtoothing" (irregular printing edge) Poor contact during exposure Check vacuum
Underexposure Perform Step Wedge Test
Light scattering Use dyed fabric
Insufficient washout Wash from both sides
Poor buildup of emulsion Improve coating technique
Fabric too coarse Use higher mesh count
Stencil softness Improper mixing of sensitizer Dissolve sensitizer thoroughly, mix well with emulsion
Underexposure Perform Step Wedge Test
Emulsion too old Review storage guidelines
Positives "yellowed" Use new positives
Excessive hummidity De-humidify area, increase exposure
Open-area "haze" Positives lack density Use new positives
Poor contact during exposure Check vacuum
Light scattering Use dyed fabric
"Pre-exposure" of coated screen Use safelights; store coated screens in dark
Over / underexposure Perform Step Wedge Test
Insufficient washout Check washout procedure
Emulsion washes or peels away during washout Coating not uniform Upgrade fabric stretching and coating procedure
Improper mixing of sensitizer Dissolve sensitizer thoroughly, mix well with emulsion
Underexposure Perform Step Wedge Test
Improper fabric preparation Degrease all fabric; roughen and degrease synthetics
Washout temperature too high Washout below 100o F
Emulsion too old Review storage guidelines
Emulsion not dry before exposure Dry screen sufficiently; use screen drying cabinet
Excessive humidity Increase exposure; dehumidify shop
Pinholes appear after exposure and washout Dirt and dust settling on drying emulsion Dry in dust-free environment
Dirt on positive or contact glass Wipe positives; use window cleaner on contact glass
Pinholes / fisheyes appear before exposure Improper fabric preparation Degrease
Shop dirt and dust Housecleaning overdue
Wet mesh Dry mesh
Dirt and dust settling in coater or emulsion container Cover coater and emulsion
Coating stroke too fast Slow down; turn screen 180o after each stroke
Air trapped during mixing Allow 1-hour (minimum) for de-bubbling on mixed emulsions
Pinholes on-press Poor coating procedure Upgrade coating method
Underexposure Perform Step Wedge Test
Incompatible ink or washout solvent Use solvent-resistant emulsion
Washout solvent or solvent ink contain water Avoid solvent storage in large drums (condensation)
Frit / pigmented inks; rough substrate Assuming proper coating and exposure, use more abrasion resistant emulsion such as FX88
Details remain closed after washout Coated screen stored too long Use freshly coated screen
"Pre-exposure" of coated screen Work under safelights; store coated screens in dark
Drying temperature too high Dry below 104oF
Overexposure Perform Step Wedge Test
Poor contact during exposure Check vacuum
Poor positive Check density
Light scattering Use dyed fabric
Poor light source Use finer mesh; use faster-exposing emulsion; upgrade light source
Incomplete washout Wash very thoroughly from both sides
Light source too close Where possible, min. exposure distance should be 1.5 times image area diagonal
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