Features

Silicone adhesives and sealants have a high degree of flexibility and a very high temperature resistance (up to 600° F), but lack the strength of other epoxy or acrylic resins. They are based upon silicone elastomeric technology.

Silicone adhesives and silicone sealants are available in two-component addition or condensation curing systems or single component RTV forms.

Room temperature vulcanizing (RTV) forms cure through reaction with moisture in the air and give off aciatic acid fumes or other by-product vapors during curing.

Technologies or cure systems for silicone adhesives and sealants are usually defined as:

• Pressure sensitive
• Radiation cured
• Moisture cured
• Thermoset
• RTV

Types

Pressure sensitive silicone adhesives and sealants adhere to most surfaces with very slight pressure and retain their tackiness. They form viscoelastic bonds that are aggressively and permanently tacky, and adhere without the need of more than finger or hand pressure.

UV or radiation cured silicone adhesives and sealants use ultraviolet light, visible light or electron beam irradiation (EB) to initiate curing and form a permanent bond without heating or excessive heat generation.

One disadvantage of UV curing adhesives is the requirement that one substrate is UV transparent. Some UV resin systems employ a secondary curing mechanism to complete curing of adhesive regions shielded from the UV light.

EB curable silicone adhesives use electron beam radiation to cure or initiate curing. The electron beam can penetrate through material that is opaque to UV light.

Reactive moisture-cured resins are single-component silicone adhesives and sealants. They are applied like hot melt adhesives until the resin reacts with moisture to crosslink and polymerize, resulting in a cured material. Some silicone adhesives and sealants (cyanoacrylates) also use a reaction with moisture or water for curing.  

Thermoset silicone adhesives and silicone sealants are crosslinked polymeric resins that cure using heat or heat and pressure. Cured thermoset resins do not melt and flow when heated, but they may soften.

RTV silicone rubbers are room-temperature vulcanizing materials. The vulcanizing agent is a crosslinking compound or catalyst. Sulfur is the traditional vulcanizing agent used with natural rubber. Silicones use moisture, acetic acid and other compounds as curing agents.

Standards

ASTM C1184 - Standard specification for structural silicone sealants.

ASTM F2524 - Standard practice for determination of volatile content for formed-in-place gaskets (FIPG) silicone adhesives and sealants for transportation applications.

FORD ESE-M4G195-C - Sealant, silicone rubber - heat resistant.

MIL-A-46146 - Adhesives - sealants, silicone, RTV, noncorrosive (for with sensitive metals and equipment).

SAE AMS3375 - Adhesive / sealant, fluorosilicone aromatic fuel resistant, one-part room temperature vulcanizing.

References

Image Credit:

Newark / element14 | Titebond