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Troubleshooting Typical Screen Printing Problems
Bubbling
SCREEN PRINTING IMAGE ISSUE: Small air bubbles on printed solids
CAUSE
HOW TO FIX
Printing speed too fast.
Reduce squeegee speed.
Too much ink deposited.
Use harder squeegee to transfer less ink.
Ink too thick (viscous).
Ink thinner additive.
Ink contains bubbles from high speed mixing.
Allow bubbles time to disperse or reduce mixer speed.
Contamination
SCREEN PRINTING IMAGE ISSUE: Non-inked spots in image section.
CAUSE
HOW TO FIX
Lint / dust in image area of screen.
Clean screen, increase humidity level. Clean work area regularly.
Contaminated substrate.
Avoid handling substrate in area to be printed. Take steps to remove dust just prior to printing.
INK SPREADING
SCREEN PRINTING IMAGE ISSUE: Thickening of image, unsharp edges, ink spreading around image edges.
CAUSE
HOW TO FIX
Ink too thin.
Ink hardener additive.
Excessive flood coat pressure pushes ink through screen.
Flood bar should not be touching the screen during the flood cycle.
Squeegee profile too rounded.
Sharpen squeegee.
Leaks, Bleeds and pinholes
SCREEN PRINTING IMAGE ISSUE: Inked spots in non-image area.
CAUSE
HOW TO FIX
Holes in non-image area of screen.
Spot out with blockout or tape or remake stencil.
SCREEN PRINTING IMAGE ISSUE: Ink leaks around image.
CAUSE
HOW TO FIX
Foreign material under stencil near image edge.
Clean underside of screen.
Ink too thin.
Ink hardener additive.
BLUR / GHOSTING
SCREEN PRINTING IMAGE ISSUE: Double edges at edges.
CAUSE
HOW TO FIX
Insufficient snap-off between product and screen.
adjust offcontact to the thickness of a nickle between the bottom of the screen and the product.
Product fixture is not the same height of the product, causing the squeegee to drop from the fixture to the product.
Make fixture same height as product. If not possible, angle squeegee approximately 20 degrees so that it cycles through the corner of the fixture. Minimize print speed.
SCREEN PRINTING IMAGE ISSUE: Image blurred and/or distorted.
CAUSE
HOW TO FIX
Press sheet sticks to mesh due to static.
Reduce speed. Increase vacuum. Increase snap-off.
Add anti-static agent to ink.Ground the table bed. Incorporate static eliminators. Mask out non-image area with paper on the underside of screen.
Ink contains bubbles from high speed mixing.
Allow bubbles time to disperse or reduce mix speed.
Printing speed too fast.
Reduce squeegee speed.Press sheet sticks to mesh due to static.
STREAKS
SCREEN PRINTING IMAGE ISSUE: Density difference across image in direction of printing stroke.
CAUSE
HOW TO FIX
Nick in squeegee blade.
Sharpen or Replace Blade.
Fault/nick on flood/coater blade.
Sharpen or Replace Blade.
Nick/scratch on press bed.
Smooth out fill in or replace flood bar.
MOTTLING
SCREEN PRINTING IMAGE ISSUE: Areas of differential ink absorption by substrate.
CAUSE
HOW TO FIX
Poor stock.
Change stock. Print clear-coat onto stock first.
Insufficient ink film.
Print thicker ink film. Use coaser mesh.
Ink too thin/transparent.
Increase pigmentation of ink.
INK DRYING IN SCREEN
SCREEN PRINTING IMAGE ISSUE: Selective parts of image areas.
CAUSE
HOW TO FIX
Ink drying in. Ink too thick.
Wash out stencil. Thin ink with solvent.
High ambient temperature.
Thin ink with retarder.
Blunt or soft rubber on squeegee.
Use sharper or harder squeegee.
INK COVERAGE FAILURE
SCREEN PRINTING IMAGE ISSUE: Second color doesn't completely cover first (second color refusal).
CAUSE
HOW TO FIX
Too much silicone in first ink down.
Change ink.
Second color too thick.
Thin/reduce ink.
Solvent release from first color through second.
Allow first color to dry properly.
Our team of knowledgeable professionals would be happy to help. Please submit a form or call 860-677-6400 if you need additional assistance.
