bioplasticsMAGAZINE_0704

Practically everybody uses them to protect sensitive
goods – high-quality stretched plastics are
undoubtedly the number one within the world of
packaging material. More and more they are replacing
paper, cardboard, tin foil and other materials. Upon applying
a particular process, mono- or biaxial orientation, the
films obtain a wealth of advantageous properties, due to a
change in the morphology of the film’s molecular structure:
• excellent mechanical properties, e.g. stiffness, tear,
shock or puncture resistance
• impermeability to moisture and water vapour
• high resistance to oils, fats and solvents, as well as to
heat and cold
• dimensional stability and scratch resistance
• attractive glossy appearance, thanks to brilliant surface
quality and high transparency
• excellent convertibility, printability and sealability.
Packaging has become a key marketing tool at the point
of sales. As a result, customers in supermarkets and
stores are placing greater emphasis on attractive packaging.
This leads to a greater demand for a variety of speciality
films:
• co-extruded multi-layer structures, up to 7 layers for
ultra-high barrier
• shrink film and sleeves for trendy, full body sleeves
• ultra-high barrier film for lamination
• bio-degradable films for environmental protection and
sustainability
• BOPA (bi-axially oriented Polyamide) film highly suitable
for freezable and cookable (microwavable) packaging
• mono-axial shrink films for bundles and labels
Orientation methods
The orientation methods applied to manufacture such
films are the film blowing process and the tenter frame
process. Blown film extrusion process is based on the
principle of extruding a tube having a thickness that is 40
– 50 times thicker than that of the film to be produced.
As part of the tenter frame process, the cast film derived
from plastic granulate by means of extrusion is stretched
in longitudinal and transverse direction to attain the required
film dimensions. This film is then processed either
sequentially or simultaneously in order to obtain a very
thin, high-rigid end film. Sequential lines first stretch the
cast film in machine direction through a system of rollers.
This stretching is achieved by different speeds between
groups of rolls. Then the film enters the tenter, an ovenlike
device, which uses two endless chains to grip and
stretch the web in transverse direction on diverting rails.
Simultaneous systems stretch the film in both directions
at the same time. The limited yield and inflexibility
of mechanical solutions led to the development of LISIM ®
Oriented
films continue
their
Processing
successful
run – even
with PLA
Article contributed by Christian Aigner,
Marketing Manager, Brückner Maschinenbau
GmbH & Co. KG, Siegsdorf, Germany
Photo: Treofan
bioplastics MAGAZINE [07/04] Vol. 2 25