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Room Temperature Vulcanizing silicones have been designed
to serve many purposes. Over the years the form and
function of these materials has evolved. Here's a
basic primer on the basic differences between the grades of
RTV and how they work.
RTV-1 SILICONE RUBBER
ELASTOSIL® RTV-1 silicone rubbers are
ready-to-use, one-part products of free-flowing to non-sag
consistency, which cure under the influence of atmospheric
moisture to form a silicone elastomer (RTV-1 =
room-temperature vulcanizing, 1 part). Thanks to the
outstanding properties of silicones, these products are
ideal for many sealing, bonding and coating applications.
Curing commences when the product is
exposed to atmospheric moisture, with elimination of
by-products. This reaction, also referred to as
vulcanization, begins at the surface of the applied layer of
silicone rubber and gradually progresses inwards. Depending
on the type of crosslinker used, the curing system can be
one of three kinds:
RTV-1 Cure System Types
- Basic or amine systems: small amounts of an
amine are eliminated.
- Acidic or acetoxy systems: small amounts of
acetic acid are eliminated.
- Neutral, i.e. oxime or alkoxy systems: small
amounts of an oxime or alcohol are eliminated.
RTV-2 SILICONE RUBBER
Condensation-Curing Systems
Condensation-curing WACKER RTV-2
silicone rubbers are composed of a rubber base and a curing
agent which contains a tin catalyst. In condensation curing,
the polymer chains bond together via a crosslinker and
ethanol is released as a by-product. Temperatures exceeding
90 °C before curing is complete result in reversion.
Properties
- RTV-2 grades contain an organo-tin catalyst
- Volatile alcohol by-product released during
curing
- At temperatures exceeding 90 °C, reversion sets
in
- When heating to boost curing rate, temperature
must not exceed 80 °C
- No inhibition of curing
- Weight loss and shrinkage occur during curing
(0.2 - 2 % linear shrinkage)
- Curing rate can be adjusted to a certain extent
by varying the quantity of the curing agent
RTV-2 SILICONE RUBBER
Platinum Catalyzed Systems
Platinum-curing WACKER RTV-2 silicone
rubbers are composed of two components, designated A and B.
In platinum-curing, polymer chains are linked through a
hydrosilylation reaction at the vinyl groups by means of the
hydrogen-containing curing agent. Some platinum-curing
silicone rubbers are available as ready-to-use one-component
products. These are cured by heating to high temperatures.
Properties
- RTV-2 grades contain an organo-platinum compound
as catalyst
- No weight loss on curing and very low shrinkage
(< 0.1 %)
- No by-products released
- Curing can be accelerated by heating (e.g. 2 min
at 200 °C)
- Pot life can be adjusted with platinum
- No reversion of curing
- Curing can be inhibited by certain substances,
e.g. compounds that contain amine, sulfur or tin
- One-component materials available
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