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SCREEN PRINTING TROUBLE SHOOTING GUIDE

Effect     Cause Remedies
Low opacity

Screen fabric too fine

Insufficient screen tension

Excessive ink thinning

Squeegee too hard, angle too acute

Insufficient snap distance

Check screening equipment

Check ink viscosity

Film defects - pinholding,

de-wetting, orange peel

Poor drying of enamel

Screen blockage

Poorly mixed ink

Excessive humidity

Contamination on work piece surface

Check dried film hardness.

Clean screen, ensure work piece is clean and dry.

Ensure ink and thinner are well mixed.

Print in air-conditioned environment.

Keep ink in sealed containers.

Bubbling    

Air entrapped in ink

Uneven ink deposit

Mix ink at lower shear rate.

Reduce flood coat speed.

Check for moisture/condensation.

Ink drips through screen

on flood-coat

Viscosity of ink too low Check ink viscosity.
Lines in enamel Defective squeegee blade Sharpen squeegee.
Thin ink deposit

Squeegee too hard

Incorrect squeegee profile

Insufficient squeegee pressure

Change squeegee.

Check screen set-up.

Thick ink deposit

Squeegee too soft

Screen too hot

Snap distance too great

Change squeegee.

Check screen/ink temperatures.

Check screen set-up.

Uneven deposit thickness Snap distance not uniform Check screening set-up and wet film thickness
Blocked screens

Moisture/condensation

Screen temperatures too low / too high

Bottles too warm

Check print room conditions.

Condition bottles.

Poor definition    

Mesh too coarse

Ink too low in viscosity for mesh

Use finer mesh.

Check ink viscosity.

Marking of enamel

Excessive handling

Insufficient drying

Reduce forces in handling process.

Ensure drying is thorough.

Ink settlement
Shelf life exceeded Rotate ink stocks.

Insufficient gloss 

enamel matte in centre

Firing temperature too low Increase heat work (temp/time) or use softer enamel.
Ghosting

Squeegee too soft

Lack of screen tension

Change squeegee.

Check screen set-up.

Poor registration

Worn machine drive chains, cams, bearing etc

Low screen tension

Insufficient snal distance

Excessive squeegee pressure

Service print machine.

Check screen/squeegee set-up.

Print migration
Wet bottles

Check ambient temperautre/bottle storage conditions.

Avoid condensation on bottles.

Print slip

Pre-heat lehr zone too cool

Poor lehr ventilation

Check lehr cycle/extraction.
Browning of enamel

Reduce atmosphere

Firing temperature too high

Check furnace atmosphere.

Use harder enamel or modify lehr cycle.

Increase bottle spacing.


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