Condensation Cure RTV Mouldmaking Silicones

RTV silicone moulding rubbers using condentaion cure are either 1-part or 2-part systems that utilise a tin based catalyst to cure. Unlike addition condensation chemistries are not kit matched, and therefore, can be used with either a standard catalyst or a specialty catalyst containing higher tin content to achieve a faster cure speed.

Properties include:

• Range of durometers/hardnesses
• Compatible with silicone fluids to increase softness
• Flexibility with mixing ratios of the base and catalyst
• Low and high tear strengths available
• Low shrinkage, below 0.5%
• Excellent dimensional stability
• Fine detail replication

CHT’s condensation cure silicones are suitable for use with a variety of casting materials including epoxy, gypsum, polyester, polyurethane, plaster, and wax.

Good tear strength is a key characteristic of mouldmaking silicones, enabling it to maintain its original form and does not easily tear when stretched or pulled. Condensation cure moulding silicones are available with low or high tear strengths to tailor to different application needs.

Low tear RTV silicone moulding rubbers are ideal for basic shapes and parts without deep undercuts, if the mold will not be used to produce a high volume of parts. These low tear grades still provide high-quality part reproduction and contribute to a lower production cost. A few applications examples include sole moulds/masters and leather reproduction.

High tear RTV silicone moulding rubbers benefit applications needing longer mould life, high volume part production, and rigid parts with deep undercuts.

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

Avoiding inhibition with condensation cure silicones

When working with condensation cure silicones, it is important to avoid inhibiting the cure process. 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.

Although cure inhibition is not a common occurrence for condensation cure grades, some sulphur containing modeling clays can slow the cure of condensation RTVs. However, the condensation cure RTV will eventually cure when the clay is removed. Inhibition can be avoided by applying a barrier coat before silicone is applied to the model.

Catalyst and specialty product enhancers

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

• Fast cure catalysts
• Additives to obtain a matte-like finish, lower viscosity, or lower durometer
• Thixotroping agents

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.