I have been tracking material throughout our plant (we are a films producer for the food industry) and I have noticed certain disturbing characteristics. At extrusion our films have good slip characteristics (allowing for appropriate bloom time)(we are currently using euricimide type slip) but sometimes after lamination our coefficient of friction (COF) dramatically increases. We use solvent based and solventless based laminators. All laminator operators complain of some build up of a film of "eraser like bits" (best way I can describe it) on their nip rolls. I have used a DSC to sample the material, which comes back as partially erucimide (slip) but mostly contains just the sealant material (generally LDPE or LLDPE). This build-up appears to be worst on a Faustel solvent based laminator, but this may be due to it is the hardest to clean. (Has anyone studied different nip roll materials or hardness for this effect?) This only appears to happen on some materials and not all the time. It does not always coincide with hotter/high humidity days.
After lamination, most of these rolls are sent to a hot room for curing. Whether there was a noticeable difference of COF at lamination or not, the final product after curing can have different/higher COFs than at extrusion/lamination. For example some rolls will be very slippery in the middle of the roll and tacky at the edges and vice versa. (This would appear to be tension related, as at extrusion the films have consistentcof across the web, any ideas here?)
I will be looking at possibly running some trials with non-migratory slips to see if this helps however they are not as effective as slip agents.
I am looking for any information if anyone has run into these problems themselves. Any help would be much appreciated.