posted October 18, 2006 06:14 PM               

We are buying a LDPE film to use in our process as a co-winding film for our main web (very sticky extrusion coating).

Lately, we have been receiving rolls that tend to stick a lot on our web. Others will slip off completely from a used co-winding film roll onto the rewinder shaft.

We tried a dyne test on the film and noticed there had been a surface treatment applied because surface tension was higher than normal LDPE. The treatment I am refering to is a corona surface treatment.

Since our specifications don't ask for a surface treatment of the film, we are trying to prove that the supplier used one.

We are not specialized in LDPE film production to know all the details so my questions are:
Is it possible the supplier always applied a corona treatment on his film to prevent rolls from telescoping?
Is it possible for LDPE (low surface energy)not to slip if you don't apply a surface treatment or add chemicals in the resin?
Is it possible that a carefully dosed corona treatment gives us just the right amount of adhesion without sticking too much or slipping?
Perhaps a problem with their corona generator caused and instability in their process, thus giving us sticky rolls and slippery ones sporadically?

posted October 27, 2006 10:54 AM               

Treating film costs money (energy), and also heats the film and the plant. It also causes Ozone waste, which is either just blown into the atmosphere (unfortunate) or run through an ozone-destruct unit (which again, cost money to maintain etc.). Because of the very tight margins, most film suppliers only treat film when it is necessary for the customer. I've never heard of treating the film to help with a winding problem, although I've only been doing this for a short time...

I wonder if your film supplier is supplying you with a consistent product, or whether they might be mixing up their formulations (slip additive sometimes but not others). Also, I wonder if their blending systems might be causing film inhomogeniety- I've seen some blenders that are very predictable as a 24-hour average but have bad batch-to-batch consistency.

What dyne level did you measure, and what is your understanding of a dyne level for untreated film?

Do you specify an untreated film? Or do you just not specify a treatment level, so the film extruder assumes it doesn't matter?