JEC COMPOSITES MAGAZINE - Issue #93 - December 2014 - 62

liner

Choosing the right release liner
The composite industry is a fast growing, very interesting market. The use of carbon fibre composites in the
aerospace industry is increasing in importance as weight
reduction becomes the central focus in order to save fuel.
This can be seen when comparing the composite content
of various airplanes. The A320 includes approximately
10% composites and the Airbus A380 increased to 28%,
but the newest models in the Airbus A350 XWB or
Boeing 787 Dreamliner families have a composite
content of more than 50%!

ost of these composite parts are
produced with prepregs (preimpregnated fibres), which are
processed in a hand lay-up process or
with an automatic tape layer (ATL). The
choice of the right carbon fibres and the
right resin is important to achieve the
desired properties for the final composite
part.

The release liner
Yet you need another material to produce
prepregs and the role of this material is
often completely underestimated: the
release liner.
The first step in prepreg production
consists in coating a resin onto a release
liner. Most of the times, the resin-coated
release liner is wound on itself and stored
in a deep freeze for later impregnation of
fibres. During the resin coating step, it is
important to create a smooth and even
coating. Reticulation and poor wetting
("fisheyes") is not acceptable. To achieve
optimal resin coating, it is important to

select the right silicone coating.
In the second step, the resin-coated liner
is unwound. It is important that the
differential release of the liner is wide
enough to prevent resin transfer from the
tight to the easy release side. The release
liner has a silicone release coating on
both sides. By adjusting the formulation
of the silicone, a wide range of release
levels from very easy to very tight can be
achieved. Determining the proper release
levels will depend on the type of resin,
the resin content, fibre stiffness and fibre
grammage.

Dr. Roland Wilberger
Head of product management
Laufenberg GmbH

nate the prepreg.
After cooling the prepreg to room temperature, the top release liner is normally
removed. The prepreg with one release
liner remaining is wound on itself or a
film is laminated onto the exposed side
of the prepreg before winding into a roll.
The next step consists in slitting the
prepreg to the desired width. The process
entails unwinding, running the material
over several rollers, slitting to width and
finally rewinding. During this process,
the prepreg remains in contact with the

Low friction
The resin-coated liner is then used to
impregnate the carbon fibres. With a
series of heating tables and calenders, the
resin is pressed into the fibres on both
sides until a certain degree of impregnation is achieved. During this production
step, it is important that the easy release
side of the release liner, which is in direct
contact with the heating table, has a low
friction level. If the friction is too high
due to an inadequate silicone coating,
the silicone can abrade off and contami-

62 jec composites magazine / No93 December 2014

4 state-of-the-art coating lines

JEC COMPOSITES MAGAZINE - Issue #93 - December 2014

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #93 - December 2014