VUV curing silicones

curing silicones without catalyst or initiator

Why use VUV lamps

UV light with a wavelength < 200 nm can break chemical bonds in many organic materials. This way it generates reactive radicals without a dedicated initiator. Consequently, it can initiate efficient reactions without a specific catalyst.

The advantages:

  • cost reduction
  • less usage of valuable resources
  • new fields of application due to avoiding harmful chemicals (e.g. food contact)

For more details about the technology please see here.

Silicone resins

There are basically two types of silicone reactive resins. Thermally curing resins rely on the reaction of silane Si-H bonds with C=C double bonds to form a Si-C bond. For a sufficiently fast reaction catalysts are added which contain a metal of the platinum group.

The second type of silicone resins contains organic functional groups which react with each other to form the crosslinks during the curing process. This can be, for example, epoxides which undergo reactions initiated by photo initiator absorbing light typically in the UV A of B range.

With VUV curing, neither a catalyst nor an initiator is necessary.

Peel test of release liners
© Fraunhofer IAP
Peel test. Measuring the force necessary to peel an adhesive tape from a release liner.
© Fraunhofer IAP
Coatings made from different resins on PET film and paper were cured with a VUV excimer lamp. Their anti-adhesive properties are visualized by the low peel force which is required to peel off an adhesive type.

VUV curing examples

UV9315 is an epoxy-terminated polysiloxane. It can be cured using a photoinitiator via a cationic mechanism. Also at higher temperature (100°C) it forms stable networks.

Using a Xenon Excimer lamp (emission 172 nm) a coating of UV9315 on a PET film can be cured within 2 s.

A vinyldimethylsiloxy terminated polydimethylsiloxane (AB109355) reacts with a polymethylsiloxane (HMS 993) at elevated temperature and catalysis by platinum compounds. Without a catalyst the reaction is rather slow. At 100°C there is virtually no reaction within 10 min.

Irradiation with a Xe excimer lamp cures a coating at 80°C within 2 s.

A coating from vinyl-polysiloxane alone on PET is cured at 80°C within 5 s.