Addition Cure Silicones

Silicone elastomers are designed with either addition (platinum) cure or condensation (tin) cure chemistry. Addition curing systems are 2-part liquid silicones that utilise a platinum catalyst to cure by either room temperature vulcanisation (RTV) or heat to accelerate cure.

It is inaccurate to say one chemistry type is better over the other. Based on application requirements, addition cure silicones feature different properties that may be the most optimal for one’s project needs compared to condensation cure grades.

Addition cure silicones do not produce by-products during the crosslinking (curing) process. The cure chemistry takes place internally, making them ideal for moulds or parts that are manufactured in a sealed environment. Addition cure silicones have very low shrinkage properties with great dimensional stability when exposed to either humidity or heat. This type of chemistry should be considered if the final mould will be stored for long periods of time between use.

Properties include:

• Extensive range of durometers/hardnesses
• Compatible with silicone fluids to increase softness
• Can be heat cured
• Casting resin resistance
• Low shrinkage, below 0.1%
• High tear and tensile strength
• Good abrasion resistance
• Excellent dimensional stability resulting in durable moulds
• Fine detail reproduction
• Food grades available

Addition cure silicones can be used with various resins and materials including concrete, stone, brick, fibre glass filled resin, polyurethane, polyester, acrylic resin, and even another addition cure silicone.

Applications: General mouldmaking, Prototyping, Dental replication, Food moulding, Architectural replication & sculpting, Composites/fibre glass part production, Tampo pad printing, Special effects, Prosthetics & orthotics

Avoiding inhibition with addition cure silicones

When working with addition cure silicones, it is important to avoid inhibiting the cure process by bringing the uncured material into contact with certain chemical compounds. The poisoning of the cure catalyst stops the crosslinking necessary for the silicone to properly cure. The result of inhibition is tackiness at the pattern interface or a total failure of the silicone to cure.

Materials known to inhibit cure are sulphur-containing modeling clays, natural rubber such as latex and rubber gloves, masking tape, amine or sulphur-containing material, condensation cure (tin-catalysed) silicones, PVC stabilizers, and epoxy resin catalysts.

Catalysts and specialty product enhancers

CHT offers various catalysts and specialty product enhancers for modifying certain physical properties in addition cure silicones:

• Accelerators to increase the cure speed
• Pot life extenders allow more time to pour and fill in large/complex moulds
• Surface coatings to lower the silicone’s surface tension
• Additives to obtain either thixotropic properties, matte-like finish, a lower viscosity, or a lower durometer

Finding the right silicone for your application is not limited to CHT’s product portfolio. Our technical team will partner with you to either modify specifications in a current product or custom formulate a new one to meet your exact requirements.

For technical assistance or sample requests, please visit our contact page.