Behaviour of Bimodal Polyethylene in Extrusion Coating, 1999 Polymers, Laminations & Coatings Conference Proceedings

Erkki Laiho

Market Development, Extrusion Coating

Borealis Polymers Oy

P.O. Box 330

FIN-06101 Porvoo

FINLAND

Jarno Ahvenlammi

M.Sc., Researcher

Tampere University of

Technology, P.O.Box 589

FIN-33101 Tampere

FINLAND

Bimodal Borstar (TM) technology produces polyethylenes by combining two reactors in a cascade. This unique combination of a slurry and a gas phase reactor gives the polymers good processability and mechanical strength, as was described at the PLC-98 Conference.

It has been assumed that during a high- temperature/rapid-cooling coating process the bimodal polyethylene transforms its structure in a different way than high pressure resins (PE-LD) or unimodal linear types (PE-LLD, PE-HD).

For this study, eight different kinds of polyethylene were tested in an extrusion coating process. The special focus of analysis was on changes in crystallinity and density. The study clearly shows that not only the density or crystallinity of the coated layer, but also the size of lamellas and their thickness distribution determine end-product properties like WVTR or heat-sealability.

It was also noticed that extrusion coating conditions like speed, melt- and chill-roll temperature had less effect on crystallinity than some earlier studies have found.