RaySi - Formulation & Coumpounding Company

RTV-2 silicone rubber and gel formulations are composed of two pourable, spreadable or kneadable parts that vulcanize after mixing at room temperature forming a material with different elasticity ranges. In addition to polysiloxane, the pourable parts generally contain:

CROSS-LINKING AGENTS
That is, hardeners (generally peroxides, silanes or polysiloxanes containing SiH) that allow the rubber to vulcanize

FILLER/FILLERS
Fillers are necessary to reinforce the silicone elastic network.

ADDITIVES
Contrary to other elastomers, the addition of additives is not fundamental as the essential properties are already determined by the polysiloxane itself but by way of example the formulation can include: catalysts, thermal stabilizers, adhesion promoters, rheological modifiers.

DYES
Silicone rubber is generally transparent or opaque but can be colored according to application needs.

RTV-2 silicones are made up of two components that can be mixed in different weight ratios, depending on the type of formulation.

COMPONENT A contains the polymer and the catalyst.
COMPONENT B contains the polymer and the cross-linker.

When components A and B are mixed, the mixture immediately begins to polymerize to form the elastomer.
Polymerization is characterized by an increase in viscosity that causes a reduction in fluidity and a decrease in plasticity.

The term POTLIFE indicates the maximum workability time of the mixture, resulting in doubling of the initial viscosity.
The material must be used (poured/mixed) before the potlife has elapsed.

The VULCANIZATION time indicates the time within which the polymer will no longer be sticky, but the final properties, however, are usually achieved after a few hours or even days.

RTV-2 silicone elastomers typically have a potlife range of 5 to 45 minutes and take 15 to 90 minutes to cure.
Potlife and cure/vulcanization time can be adjusted by selecting a “slow” or “fast” curing agent and varying the mixing ratio.
The greater the amount of curing agent used, the shorter the curing time will be.

Recommendations:

• With a low amount of curing agent (component B), the cure will be unsaturated and the rubber will be soft or even tacky and with low mechanical strength.
• With a high amount of curing agent, the resulting elastomer will have decreased release properties, increased hardness, reduced elasticity and high possibility of embrittlement.
• The rate of cure can be slightly accelerated by increasing the temperature. However, heating should not exceed 80 °C before complete cure, otherwise the silicone rubber may be destroyed. At temperatures above 80 °C, the cross-linking reaction is reversed and the product will be sticky or will return to a soft state.