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. |
