Silicone Cure Systems
Silicone elastomer can be crosslinked ("cured" or "vulcanized") into solid forms through a variety of cure systems.
The most common curing systems are: 1) addition cure chemistry (platinum catalyst) which does not require moisture or open air, and
2) condensation cure (tin catalyst) chemistry which requires airborne moisture.
Dual cure systems also exist, which are formulated to react with both ultraviolet light and humidity (water vapour in the air). Dual cure systems are especially useful with complex shapes as when exposed to UV light (of the appropriate wave length and intensity), it cures rapidly (seconds) to produce a durable and flexible optically clear, non-yellowing and chemically resistant sealant, adhesive or coating. Silicones also exhibit excellent electrical insulation properties. The moisture cure portion of the dual cure feature ensures that all of the material cures where UV exposure is difficult or imperfect. Pure RTV (Room Temperature Vulcanization) cures can usually be accomplished within 24 hours at ambient temperatures or faster at elevated temperatures.
Condensation Cure
Condensation cure systems use humidity during curing and cannot be accelerated using heat (excessive heat can be detrimental). Small amounts of by-product are also produced. The cure process will only take place if the material is open to the atmosphere and curing will be adversely affected if access to humidity is removed prior to the completion of the cure process. This curing method is commonly used for 1-Part sealants & coatings and 1 & 2 Part potting encapsulants.
Silicone elastomer can be crosslinked ("cured" or "vulcanized") into solid forms through a variety of cure systems.
The most common curing systems are: 1) addition cure chemistry (platinum catalyst) which does not require moisture or open air, and
2) condensation cure (tin catalyst) chemistry which requires airborne moisture.
Dual cure systems also exist, which are formulated to react with both ultraviolet light and humidity (water vapour in the air). Dual cure systems are especially useful with complex shapes as when exposed to UV light (of the appropriate wave length and intensity), it cures rapidly (seconds) to produce a durable and flexible optically clear, non-yellowing and chemically resistant sealant, adhesive or coating. Silicones also exhibit excellent electrical insulation properties. The moisture cure portion of the dual cure feature ensures that all of the material cures where UV exposure is difficult or imperfect. Pure RTV (Room Temperature Vulcanization) cures can usually be accomplished within 24 hours at ambient temperatures or faster at elevated temperatures.
Condensation Cure
Condensation cure systems use humidity during curing and cannot be accelerated using heat (excessive heat can be detrimental). Small amounts of by-product are also produced. The cure process will only take place if the material is open to the atmosphere and curing will be adversely affected if access to humidity is removed prior to the completion of the cure process. This curing method is commonly used for 1-Part sealants & coatings and 1 & 2 Part potting encapsulants.
|
Condensation Cure 1 Part Systems |
|
| Advantage | Disadvantage |
| Easy to Apply | Max 10mm thickness |
| No mix - no mix error | Fixed curing speed |
| Easy dispensing | Narrow viscosity range |
| Reversal of cure possible | |
Addition Cure
Addition cure uses a platinum catalyst to initiate curing and do not produce any by-products. Once catalised, the cure will complete, even in a sealed enclosure. No atmospheric exposure is required. 2-Part systems can be designed to cure at room temperature and heat can be used to accelerate the cure if required, without any detrimental effect. 1-Part systems normally require heat before they will cure.
The platinum catalyst is susceptible to attack from certain chemicals which will lead to incomplete cure. Uncured platinum catalyst should not contact compounds containing:
- nitrogen - sulphur - phosphorus - arsenic - organotin catalysts - PVC stabilizers
- epoxy resin catalysts - sulphur vulcanised rubbers - condensation cure silicone rubbers
(Note: Alkoxy cured RTV's do not cause contamination).
These systems are produced in balanced batches: It is important that two components are thoroughly mixed and the correct mix ratio followed. Its is normally not recommended to use materials from different batches.
Addition cure uses a platinum catalyst to initiate curing and do not produce any by-products. Once catalised, the cure will complete, even in a sealed enclosure. No atmospheric exposure is required. 2-Part systems can be designed to cure at room temperature and heat can be used to accelerate the cure if required, without any detrimental effect. 1-Part systems normally require heat before they will cure.
The platinum catalyst is susceptible to attack from certain chemicals which will lead to incomplete cure. Uncured platinum catalyst should not contact compounds containing:
- nitrogen - sulphur - phosphorus - arsenic - organotin catalysts - PVC stabilizers
- epoxy resin catalysts - sulphur vulcanised rubbers - condensation cure silicone rubbers
(Note: Alkoxy cured RTV's do not cause contamination).
These systems are produced in balanced batches: It is important that two components are thoroughly mixed and the correct mix ratio followed. Its is normally not recommended to use materials from different batches.
|
Condensation Cure 2 Part Systems |
|
| Advantage | Disadvantage |
| Tolerant to catalyst ratios | Small increase in shrinkage |
| Low risk of cure failure | Cure reversal possible |
| Deep section cure | |
| Cure acceleration possible | |
|
Addition Cure 1 Part Systems |
|
| Advantage | Disadvantage |
| Easy to Apply | Require heat to cure |
| No mix - no mix error | Adhesion harder to achieve |
| Thin & Thick section cure | Prone to cure failure |
| Good physical strength | Shorter shelf life |
|
Addition Cure 2 Part Systems |
|
| Advantage | Disadvantage |
| Excellent deep section cure | Prone to cure failure |
| Pot life extension | Requires accurate mix |
| No cure reversal | Good adhesion difficult |
| Cure acceleration with heat | |
| Optically clear available | |
| Low shrinkage | |
| 1 Part RTV Cure Methods | ||
| Mechanism | By-Product | Effect |
| Acetoxy | Acetic Acid | Corrosive |
| Oxime | Ketoxime | Mild Corrosive |
| Alkoxy | Methanol | Non Corrosive |
| Acetone | Acetone | Non Corrosive |
1-Part condensation cure products should not be used where the depth of potting is more than about 10mm as it will cure with a membrane and prevent the remaining material underneath the membrane from completing the cure process.
1-Part RTV silicones can use a variety of cross-linkers and these cross-linkers produce by-products: the Acetoxy and Oxime can be harmful to electronic components: Alkoxy and Acetone cure 1-Part RTV's should only be used for potting and encapsulation of electronics.
Possible Cure Reversal: - condensation cure systems using organotin catalyst can chemically break down and revert to liquid form. This process may occur when the silicone is contained in a totally closed or hermetically sealed unit which is at continuous elevated temperatures and for long periods of time (several months above 60ºC). If the material is allowed to breathe to the open atmosphere the cure reversal will not occur and resistance to high elevated temperatures (up to 300ºC) is achieved.
1-Part RTV silicones can use a variety of cross-linkers and these cross-linkers produce by-products: the Acetoxy and Oxime can be harmful to electronic components: Alkoxy and Acetone cure 1-Part RTV's should only be used for potting and encapsulation of electronics.
Possible Cure Reversal: - condensation cure systems using organotin catalyst can chemically break down and revert to liquid form. This process may occur when the silicone is contained in a totally closed or hermetically sealed unit which is at continuous elevated temperatures and for long periods of time (several months above 60ºC). If the material is allowed to breathe to the open atmosphere the cure reversal will not occur and resistance to high elevated temperatures (up to 300ºC) is achieved.
Silicone Technologies
Cured Silicone Rubber Products
Silicone Tape - Silicone Rubber Coated Fiberglass Fabrics
Silicone Rubber Coated Fiberglass Sleeves - Silicone Rubber Coated Fiberglass Tapes
Silicone Rubber Coated Fiberglass Ropes - Silicone Rubber Tubing, Caps & Plugs
Silicone Foam / Silicone Sponge / Silicone Sheet
Silicone Tape - Silicone Rubber Coated Fiberglass Fabrics
Silicone Rubber Coated Fiberglass Sleeves - Silicone Rubber Coated Fiberglass Tapes
Silicone Rubber Coated Fiberglass Ropes - Silicone Rubber Tubing, Caps & Plugs
Silicone Foam / Silicone Sponge / Silicone Sheet
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AB Tech's silicone products have the high-temperature and chemical
resistance of glass along with the versatility and flexibility of plastics
resistance of glass along with the versatility and flexibility of plastics
Uncured Silicone Products
Silicone Adhesives & Silicone Sealants - Silicone Gels - Silicone Conformal Coatings
Silicone Dip - Silicone Paint - Silicone Ink - Packaging Options
Silicone Adhesives & Silicone Sealants - Silicone Gels - Silicone Conformal Coatings
Silicone Dip - Silicone Paint - Silicone Ink - Packaging Options
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