JEC COMPOSITES MAGAZINE - Issue #111 - March 2017 - Special JEC World - 28

MANUFACTURING resin

Fig. 4: Typical epoxy system viscosity curve during the sheet production, maturation and moulding phases of SMC processing

Fig. 5: Sample component demonstrating a seat
frame structure with approximately 0.35m2 of
surface area and an initial SMC charge area of 25%

located only along the main load paths,
would optimize weight, cost and packaging parameters.
Process on existing SMC lines
The new Hexion epoxy-based systems can be processed on any existing
SMC line without major modifications (Figures 2 & 3). For ease of use,
each system simply consists of a resin,
a hardener and an optional internal
mould release agent. Additionally, additives such as wetting or degassing
agents may further increase performance. Components may be blended using standard mixing equipment.
Resin films are produced at ambient
or slightly elevated temperatures and

are then used to impregnate the fibres
and form the SMC sheets. Especially
with carbon fibres, some heating of the
impregnation zone has proven helpful
in achieving the best fibre impregnation. After impregnation, the sheets are
rolled and stored for maturation as with
conventional UP and VE materials.
Epoxy SMC matures through a B-stage
epoxy reaction. This reaction can be
moderated by ambient temperature
control and is dependent upon the
compound's fibre type and resin content. After maturation, these materials
may be stored at ambient temperatures
for 2-3 weeks. Alternately, the matured
sheet may be frozen to extend the shelf
life to 6 months.

minutes. If high surface quality is needed, starting with the lower temperature
is recommended. If an internal mould
release agent is used, the parts can
be easily removed from the tool after
moulding. During initial trials of both
glass and carbon fibre SMC sheets, it
was possible to mould parts with completely filled ribs and bosses, as shown
in Figure 5.

Figure 4 shows the various stages of
this type of epoxy resin's viscosity development. The material has been designed to mimic the typical behaviour
of standard UP and VE formulations for
easy handling.

Conclusions and outlook
Hexion's new styrene-free epoxy system
for SMC achieves best-in-class performance. The product is easy to handle,
can be processed on standard SMC
lines with only minor modifications,
and comes with experienced processing, troubleshooting, and moulding
assistance. Epoxy SMC is suitable for a
wide range of semi-structural and structural applications such as rear floors,
electrical vehicle battery enclosures,
spare wheel tubs, seat structures, hood
inners and more.

After reaching the target viscosity
level, epoxy SMC can be compression-moulded using the same equipment as for traditonal SMC moulding.
Ideally, chrome-plated steel moulds
with shear edges can be employed.
Applying a vacuum during the compression moulding step is important to
help avoid air entrapment, which can
result in blisters on the moulded parts.
Typically, epoxy SMCs can be moulded
at 150°C for 3 minutes or at 140°C for 5

More information:
Hexion.com/StyreneFreeSMC
or Hexion.com/contacts
References
[1] Plastics Europe - Cefic - UP
Resin Group Occupational exposure to
styrene. Technical Bulletin.
[2] Rasoul, H.A.A. et al. (2016),
Low VO/Low Odor SMC for Interior
Applications. Automotive Composites
Conference and Exhibition (ACCE),
conference proceedings, Novi, Michigan.

jec composites magazine / No111 March 2017

http://www.Hexion.com/StyreneFreeSMC http://www.Hexion.com/contacts

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