JEC COMPOSITES MAGAZINE - Issue #109 - November/December 2016 - 26

MANUFACTURING RTM

Recent advances in powder coating
technology for the RTM process

anabel Crespo soler
Senior Researcher
Ecogel-Cronos Project Technical Coordinator
AIMPLAS Composites Department

The EU regulation on the CO2 emissions of new cars sets out the
targets for the average new car fleet across Europe to achieve
95g/km by 2020. The challenge is to reduce the weight of vehicles to
meet the EU CO2 emissions targets without incurring a cost penalty
and, ideally, achieving cost savings. The business opportunity is
to implement technologies and design solutions to deliver vehicle
weight savings that are market ready for 2020. Major weight savings can be achieved by replacing conventional materials with composite materials. Composites can reduce vehicle weight, increase
fuel efficiency and improve power-to-weight ratios, leading to an
overall better performance.

Powder gelcoat

major challenge to the use of
composite materials has been
the ability to reduce production
cycle times. In this context, the
Ecogel Cronos project aims to develop
an innovative and high-productivity
resin transfer moulding (RTM) process
through the use of fast-curing "zero VOC
emissions" powder gelcoats and electrically-conductive hot skin mould technologies based on carbon-fibre plastics
laminates (CFP laminates).
The integration of both technologies in a
suitable way will help modify the current
RTM process to enable the use of powder
gelcoats in production, obtaining a highproductivity RTM line to mass produce
parts for the transport sector. Two products representative of the advantages of
this new production line were developed
within the project as demonstrators: a
fully-finished agricultural equipment part
and a composite automotive part ready
for electrostatic painting.

Just like the painting industry started, in the
1950's, to use dry powders to replace existing liquid paints, the liquid gelcoats used in
the composites industry may be replaced
with a proper dry powder technology.
A powder gelcoat is a compound made of
solid ingredients intimately blended and
ground to obtain a very fine powder. The
type of ingredients used in the formulation may vary depending on the required
properties of the coating. Powder gelcoats
chemically react with the substrate, creating an integral laminate. These coatings are
applied on the mould with conventional
powder spraying equipment. When the
coating/substrate curing cycle is complete,
the finished part, fully-painted on the exterior face, can be removed from the mould.
Unlike liquid gelcoats, a powder gelcoat
exhibits a very short curing time of just a
few minutes under suitable temperature
conditions (around 130°C). This reduces
the production cycle time tremendously
as the curing time of liquid gelcoats is
typically around several hours at room
temperature. Unlike liquid gelcoats,
which require a "tacky state" to get a good
interaction interface between the gelcoat

jec composites magazine / No109 November - December 2016

and the injected resin, the powder gelcoat
film reacts with the resin used in the injection unit, forming a chemical interphase
and, consequently, producing unbeatable
adhesion properties between the gelcoat
and the injected resin at any time after
film formation.
A very important aspect of powder gelcoats based on unsaturated polyester
resins is that, being free of solvents and
volatile compounds, the effective yield
in grammes per square metre is always
higher than that of a liquid gelcoat (approximately 1:4) (Fig. 1).
Powder gelcoats are used in SMC (sheet
moulding compound) processes, but the
development of new powder gelcoats for
RTM or infusion processes plays a vital
role in cost reduction, ensuring the required quality and high productivity rates
for automotive applications in the composites industry. A range of fast-curing
power gelcoats for the RTM industry was
developed as part of the Ecogel Cronos
project. The first step was the formulation
of an unsaturated polyester powder resin
system. Different systems were developed
and combined with suitable additives in
order to obtain highly-reactive, stable and

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #109 - November/December 2016