JEC COMPOSITES MAGAZINE - Issue #119 - March 2018 - 44

MANUFACTURING curing

GRP composite manufacturing optimization:
opportunities with UV curing

dr. dAvid beke,
New Business Development Manager
luc boogAerts,
Technical Services & Business
Development Specialist
dr. pAtrice roose,
Senior Research Scientist
dr. Jon sHAw,
Manager Radcure Technical Services
and Business Development
Allnex

hereas traditional resins are
converted from a liquid to a
solid material through solvent removal, heat-induced crosslinking or oxidation for air-drying systems,
a liquid formulation of acrylate resins
will transform into a solid crosslinked
network upon exposure to UV light.
Typically, the UV light decomposes
a photoinitiator into primary radicals
that initiate a radical chain reaction of
the acrylate double bonds, a process
known as "free radical polymerization".
As a result, a highly crosslinked system
is formed in a few seconds.
Since its introduction in the 1960s,
UV curing technology has gained
acceptance in the coatings and graphics
industry owing to its short curing cycles, its ability to meet the performance
requirements for most applications
by tuning the chemistry and its very
limited Volatile Organic Compounds
(VOC) emissions.
For composite applications, fairly thick
parts and layers need to be manufactured. With the introduction of phosphine-oxide-based photoinitiators such
as bisacylphosphine oxide (BAPO),
which are particularly efficient for
deep through-cure of laminates when

Composite manufacturers are facing increasing pressure to improve
operational efficiency, identify saving opportunities and reduce their
ecological footprint, without compromising material performance. The
implementation of an ultraviolet (UV) curing manufacturing process is
proving to be an effective step towards these goals. Before considering such process improvements, manufacturers and OEMs should be
aware of the benefits and boundaries of the current state of the art
in UV curing technology.
combined with the right resin compositions, UV curing has emerged as a
cost-effective solution in a number of
applications.
A broad range of UV-curable resins is
available today, allowing to meet the
basic requirements of many demanding
applications:
- The viscosity of UV-curable resins
is often adjusted using non-volatile reactive diluents, which are
incorporated into the network and
contribute to the properties of the
end material.
- Polyester acrylates exhibit good
wetting and adhesion properties.
Diluting unsaturated polyesters
with reactive diluents can be a good
approach to eliminate styrene.
- Epoxy acrylates combine good
toughness with excellent chemical
resistance and mechanical properties according to the type of modification. These resins are similar to
the well-known vinylester types.
- Urethane acrylates cover a broad
range of properties, combining for
example hardness and resistance
to failure (flexibility). Aliphatic
urethane acrylates are essentially
non-yellowing
with
excellent
weathering properties. In contrast,
aromatic urethane acrylates are
less weathering-resistant but more
cost-competitive.

jec composites magazine / N°119 March 2018

Benefits and boundaries: when to
consider using UV technology?
The arguments to implement UV technology in composite manufacturing can
be compelling, but UV curing will not
suit all applications. Successful implementations of a UV-curing composite
manufacturing process start with a
careful translation of the limitations
and benefits of the technology to the
specific application.
A first benefit is that, by eliminating
VOCs, manufacturers reduce their ecological footprint, eliminate regulatory
risks and avoid the costs that come with
using solvents (processing). Secondly,
by replacing the heating chamber with
a UV lamp, energy consumption is
drastically reduced. Thirdly, since UV
formulations are one-component systems, they are not restricted by pot life,
which means cleaning labour is avoided
and waste is reduced. As the crosslinking is driven by exposure to UV light,
independent from ambient conditions,
the curing process is consistent and
well-controlled. Finally, the speed of
curing enables high-throughput manufacturing lines. Hence, retrofitting a
line to UV curing can be an effective
way to increase capacity. For new lines,
investment costs are contained thanks
to the absence of a heating chamber,
while still bringing a high throughput
process on limited floor space.

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #119 - March 2018