Opacity

1. Check ash content of sheet.
— if it is low, dope up system in the stock preparation area.
2. Optimize filler dispersion and first-pass retention.
— increase or decrease flow of retention agent as needed
3. Consider addition of sodium aluminate to system.
4. Check the white water pH.
— maintain the pH as high as operating conditions will permit.
5. Check flat box vacuum.
— use as little vacuum and as many boxes as possible.
6. Adjust table setup.
— check foil positions and blade angles.
— need to close up sheet and still control drainage rate.
— lower some drainage elements if possible.
7. Increase refining to permit better filler retention.
— higher consistency, fibrillating refining promotes retention.
8. Check white water system to be sure there are no excessive losses.
— check saveall efficiency to maximize fines recovery.
9. Slow down machine.
10. If low opacity persists on all heavily filled grades, consider possibility of a finer weave forming fabric.
— check condition and wear of machine clothing.
11. If ash content is at target or above, investigate possible furnish change to higher opacity pulps.
12. Improve sheet formation.
— close up structure and get better first-pass retention.
13. Reduce size press solids and/or pick-up if other tests permit.
— too much surface sizing tends to lower opacity.
14. Consider furnish change to hardwood or better forming pulps.
— good formation helps opacity.
— increase broke percentage.
15. Check and adjust calender temperature and pressure.
— excessive calendering lowers opacity.
Related subjects include, Ash content and Filler content varying.