AQ Coating Build Up
Currently we are getting some coating build up on the tail edge of the sheet (in the spot where the packing drops off) on our Lithrone 28 with 3 roller Komori Coater (Steel pan roller, rubber metering and steel aplicator roller). This isn't usually a problem, but we have a very large run of 80# Text Gloss, and it can cause the sheets to stick together if we don't shut down to clean the coater blanket at regular intervals.
-Checked blanket and packing thickeness
-Packing is cut sharply and cleanly
-Blanket to impression set at "kiss" nip squeeze
-Adjusted aplicator roller to 5mm squeeze to blanket, which is the setting the maual has listed
-Adjusted aplicator roller to 4mm (just in case)
-Checked coating viscosity
-Tried reducing coating feed drastically
Any comments or suggestions as to something else I could try? Thanks,
We have SM102s with the old school blanket roll coaters, just two rollers-coating pan and applicator. So our setting may be different than yours. Our coaters are real sensitive to pressure so we kiss coat everything.
When we have problems like this we check everything- viscosity, roller settings etc. sounds like you've done all of that. From there we make up a new blanket and packing (they don't last forever even if they look ok, we date them and after a month toss them out), torque the blanket correctly, back the applicator off completely then we run the press with the coating unit on only. We gradually bring the applicator in contact with blanket until we achieve a uniform coating film thickness. This way we know we are "kiss" coating.
For us, if we have coating build up on the tail edge it is 99% due to to much pressure somewhere- usually the applicator to the blanket. The coating is being squeegeed off to the tail edge if that makes sense.
When the kiss coat doesn't work something else is wrong, usually mechanical. One of our presses was having coating build up on the tail edge no matter what we tried. The clutch for the applicator had gone bad causing the the applicator roller to drag across the blanket, building up coating on the tail edge. An easy way we check for this on our Heidelberg's is if the applicator roller can turn backwards the clutch is bad.
Good Luck, sometimes it's the job and there's not much you can do. We clean the coating blanket every lift even when everything is perfect.
Maker sure stock is long enough. If your stock is shorter than your coating blanket then you will get build-up.
if room allows on the sheet you can try tapering off the blanket packing so that the tail coating edge is gradual. You might also want to try experimenting with different coating blankets with various "release" properties
Coating may be too thin. We have a three roll coater on one of our presses and it runs better with a thicker viscosity coating. Try adjusting the applicator roller.Back off the stripe to the blanket until it breaks up then bring it up just until it prints evenly. Meter roller may also need to be tightened up. If our press is slinging we can tighten the meter and speed it up to get a thinner film but the same amount of coating and because the roller is turning faster it is less likely to skid off the tail on the blanket.
Your applicator roller may also need to to be tightened to the drive roller.