What Are The Differences Between Platinum-Cure And Tin-Cure Silicone Mould Rubbers?

The chemical difference between platinum-cure (addition cure) and tin-cure (condensation cure) silicone mould making rubbers is in the metal used to catalyse (cure) the base rubber. The metal Tin is used to cure tin silicone, and Platinum is used to cure platinum silicone rubber. For this reason, tin-cure silicone rubbers are usually significantly less expensive than platinum-cure ones.

Performance Differences

Inhibition

All mould making rubbers may be subject to cure inhibition (see Why Didn’t My Rubber Cure) by contaminants on the surface of a model being used for mould making. Silicone rubber is sensitive to sulphur that can be found on different surfaces – present in some types of modelling clay. Platinum-cure silicone rubbers are critically sensitive to sulphur and will not cure under any circumstances when exposed. Tin-cure silicone can cure over models containing sulphur if the model surface is first thoroughly sealed with a spray such as SprayOn SP322.

Shrinkage

A major difference between these two silicone systems is shrinkage of the cured rubber over the short and long term. Tin-cure silicone rubber moulds generally exhibit higher shrinkage over time depending on:

• The type of mould rubber being used
• Material being cast into the rubber mould
• Mould configuration, and other variables.

Library Life

Library Life refers to how long a rubber mould will last in your “mould library”, just sitting on a shelf and not being used.  Some mould rubbers last longer than others.

Tin-cure silicone rubber moulds have a limited library life. Depending on the specific tin-cure silicone, the library life of a rubber mould can be as little as 12 months, which may be acceptable if your project is short term. At the end of a rubber mould’s library life, the mould will tear easily and become unusable.

Platinum-cure silicone has a relatively long library life that is measured in decades. Because of this longevity, museums choose platinum-cure silicone rubbers to make moulds of valuable artifacts and works of art.

Production Life

The number of castings which you can expect to get out of a rubber mould before it becomes unusable, is often referred to as the “Production Life”.

When choosing which silicone rubber (tin or platinum) will give you the longest life for production casting,  you need to consider the different variables as this is usually application specific. It is important to consider:

• What type of mould are you using?
• What are you casting into the mould (wax, gypsum, concrete, resin, etc.)?
• Did you use a release agent?
• How long are castings left in the mould?

TIP: To determine which rubber mould material is right for your project, contact the Neill’s Materials technical support team.

Original Source: Polytek Development Corp.