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Direct Stencils (Capillary & Emulsions). Fault finding guide. Detail filling in. Cause Use of white mesh. Remedy Use dyed mesh and increase exposure. UV light. UV light. Detail filling in. Cause Poor contact between positive and stencil. Remedy Improve vacuum

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Direct Stencils (Capillary & Emulsions)

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    1. Direct Stencils (Capillary & Emulsions) Fault finding guide

    2. Detail filling in

    3. Cause Use of white mesh Remedy Use dyed mesh and increase exposure UV light UV light Detail filling in

    4. Cause Poor contact between positive and stencil Remedy Improve vacuum Check positive is right reading Ensure backing sheet removed Positive Detail filling in Undercutting caused by positive in poor contact with the stencil Positive in good contact with the stencil UV light UV light

    5. Positive Positive UV light UV light Fine detail filling in Cause • Light undercutting on high Rz stencil Remedy • Use Capillex • Use higher solids stencil • Add additional wet on dry coats

    6. Cause Poor light source geometry Remedy Increase lamp distance Reduce reflected light UV light Light more perpendicular to the stencil Detail filling in

    7. Dust Positive UV light Detail filling in Cause • Dust between positive and stencil Remedy • Ensure positive and stencil are clean by using a clean room wipe or Teknek roller

    8. Detail filling in Cause • Over exposure • Poor wash out Remedy • Reduce exposure • Many stencils benefit from a final wash with a high pressure gun at 1m distance, especially water resistant stencils No resolution improvement at different exposures indicates a washout issue

    9. Badly decomposed diazo Good diazo Detail filling in Cause • Diazo decomposed by heat or age Remedy • Ensure diazo is stored between 3oC and 20oC and is within 2 year shelf life

    10. Cause Gross over-exposure Excessive drying temperature Coated screen fogged by light Low density positive Remedy Reduce exposure Dry coated screen at max. 40°C Store coated screen in dark or under safelight Re-make positive Difficult to washout

    11. Pinholes - Emulsions Remedy • Ensure emulsion fills the mesh during print side coatings • Ensure the pot has fully degassed before coating • Reduce coating speed • Metal stirrers gouge the sides of the pot on sensitising. Use the wooden stirrer provided Cause • Air entrapment during coating • Air entrained in the emulsion • Air developing in the trough • Bits in the emulsion

    12. Strong stencil with all diazo sites cross linking PVOH Correctly dried stencil UV Diazo Weak stencil with some diazo sites reacted with water Underdried stencil Poor Adhesion Cause • Inadequate drying prior to exposure Remedy • Dry coated screens thoroughly. • Do not dry unexposed screens in the same cabinet as wet screens

    13. Cause Under-exposure Remedy Use Autotype exposure calculator to find correct exposure time Ensure has correct UV output and lamp has not aged Poor Adhesion

    14. Cause Under exposure Remedy Increase exposure time Poor Adhesion

    15. Cause Poor edge quality of positive Incorrect exposure Use of white mesh Remedy Remake positive Expose for optimum time Use dyed fabric Poor Definition

    16. Cause Under-exposed stencils are more difficult to reclaim A and B Hardener used Stripper incorrect concentration Stencil fusing Remedy Increase exposure to optimum If reclaim is required do not use A and B Hardener Check stripper is correct concentration 2-4%, for very water resistant stencils err on the higher side, so 1:25 stripper concentrate should be used at 1:15 dilution Change solvents used with the stencil Mesh difficult to reclaim