SOLID AND LIQUID SILICONE RUBBER ... - Wacker Chemie

6.1.
POST-CURING
Ideally, silicone rubber articles do
not need secondary finishing. But
in many cases the material must be
post-cured. That involves heating
at a high temperature for a defined
time.
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Why is Post-Curing necessary?
Post-curing is performed to achieve
an improvement in the mechanical
properties (e.g. a particularly low compression
set), and to remove volatiles
(by-products from the crosslinker
chemicals and low-molecular polymer
components). For e.g. food-contact
applications, post-curing is recommended
or even essential in order to
meet legal requirements.
• Peroxide-curing rubber:
Post-curing serves principally to
eliminate by-products from the
peroxide curing reaction. When
ELASTOSIL ® AUX Crosslinker E is
used, by-products migrate to the
cured rubber surface over several
hours, and can be seen as white
crystal deposits on the surface
(blooming). In the case of
ELASTOSIL ® AUX Crosslinker C1
or C6, the by-products impart a
characteristic odor to the cured
rubber, which can be removed by
post-curing.
• Addition-curing platinum-catalyzed
rubber:
In this case, curing does not form
odor containing by-products. But
post-curing is still recommended if
the silicone article is intended for
use in sensitive areas, such as food-
contact or medical applications. In
such cases the relevant recommendations
FDA 1 or BfR 2 or E.P. 3.1.9 3
must be followed.
Removing Defects
Other work steps may be necessary in
the following cases:
• Correcting flash or defects (cryogenic
deflashing or sanding down)
• Removing sprue waste and talc
Our experts will be glad to help you set
up your production plant
to manufacture products that meet your
demands, and eliminate unnecessary
production steps, e.g. by means of test
series in our pilot plant or on-the-spot
advice.
1 FDA Chapter 21 CFR § 177.2600 Rubber Articles
Intended for Repeated Use.
2 BfR recommendation XV. Silicones.
3 E.P. 3.1.9: European Pharmacopeia 5.0, Chapter 3.1.9.