JEC COMPOSITES MAGAZINE - Issue #80 - April 2013 - 60

prepreg

Fig. 1: Release liner and prepreg

between the release value of each side
is called the release differential.
The “tight” side has the highest
peeling force. This side will be coated
with the composite matrix. The
opposite side with a lower peeling
force is called the “easy” side.
The release differential between easy
and tight side can range from 1-2
to 1-30 depending on the end-use
market. It is a key parameter as it will
ease peeling at the product separation
step.

an even coat of resin.
- At the impregnation (prepregging)
stage: yarns or fabrics (carbon,
glass…) are impregnated with the resin on both sides, usually designated
as top and bottom. After transferring
the resin from the release liner to the
yarn, the top release liner is generally
rewound while the bottom is wound
with the impregnated yarns or fabrics
in a roll form named prepreg.
- At the lay-up stage: rolls of prepreg
are then converted into final products. There are two main conversion processes: hand lay-up (HLU),
used in all sub-segment markets, and
automated lay-up methods such as
ATL (automated tape laying) or AFP
(automated fibre placement), used in
aerospace and wind energy.
The appropriate release liner will be
chosen according to its usage: resin
tackiness, top or bottom, coating
technique, hygrometry conditions or
lay-up process.

The essential role
of release liners
At each stage of the manufacturing
process, perfect control of release
liner properties is essential to pro-

Three silicone formulation technologies are available on the market:
solvent-based, solventless and emulsion. Gascogne Laminates provides
a complete portfolio of solutions
relying on these three technologies,
allowing the use of a wide range of
backings.

Use of release liners in
prepreg manufacturing
Release liners are used as process
and/or carrier liners in the manufacturing of thermoset prepregs:
- At the filming stage: a thermoset
resin (epoxy, BMI…) is coated on
the tight side of the release liner.
Different coating techniques can be
used: direct, reverse or doctor blade
coating. The objective is to lay down

Fig. 2: Impregnation stage at HEXCEL – Dagneux
(France) with top and bottom release liners

60 jec composites magazine / No80 April 2013

duce high-quality prepregs and allow
smart prepreg manufacturing and
converting.
For instance, release liner caliper
consistency is fundamental to obtain
an even thermoset resin coating
weight at the filming stage. Perfect
control of the required release level
will enable an optimum resin transfer
rate onto fibres at the impregnation
stage. An excellent silicone polymerization rate will prevent the prepregs
from being contaminated. Finally,
an optimum dimensional stability
will impact the prepreg flatness and
prevent it from curling.
A release liner is not just a waste
material, it is a process efficiency
enhancer!

Future trends in release liners
In daily contact with prepreg customers, Gascogne Laminates listens
carefully to the market in order to
identify and understand composite
trends related to material and process
evolutions. For instance, performance/cost is a key ratio in the sports
and leisure business. This is why
downgauging the fibre areal weight
(FAW) is always carefully studied for
a given application and needs to be
translated accurately in all steps up
from the release liner design.
Aerospace is the most advanced market segment with respect to automated prepreg lay-up. For instance, the
performance of ATL heads is driven
by enhancing their efficiency in a
high-precision environment. Thanks
to the right selection and combination of release agent and substrate,
release liners will not only prevent
disruption in this particular case, but
also allow the manufacture of worldclass quality prepreg parts. Gascogne
Laminates’ innovation is clearly
geared to designing the next generation of release liners to cope with the
ever-changing prepreg technology.

“Intelligent” release liners for
specific end-use markets
While most manufacturers provide a

JEC COMPOSITES MAGAZINE - Issue #80 - April 2013

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #80 - April 2013