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UV protection in thin layer PU coating

UV protection in thin layer PU coating

(OP)
Hi,

I need to coat a solvent borne 2K polyurethane coating onto a flexible plastic (PET) surface. The coating thickness can't be more than 10-12 micron in order to stay flexible.

The coating will have some light stabilisers (HALS) to protect the coating itself but I also have to add protection for the plastic substrate. I am trying to find out what will work better for a thin coating like this. The solution can be UV absorbers like Tinuvin (BP, BTZ) or it can be an inorganic blocker, like titanium dioxide or zinc oxide. Or perhaps something else I don't know about.

My priorities are:

1/ maximum possible protection of the substrate within a 12 micron coating thickness
2/ minimum degradation of the coating (flexibility, elongation, adhesion) over 1 years of continuous outdoor use in a south florida environment
3/ minimum increase of coating viscosity

The coating is not pigmented. Clarity or gloss is not an issue and it can become translucent but should not become pigmented. Carbon black is therefore not an option.

I can't add anything to the plastic substrate, as this is not produced by us.

Any advice will be much appreciated !



RE: UV protection in thin layer PU coating

The UV absorbers in the urethane may not have been intentionally optimized to protect your plastic but you are unlikely to improve the protection by changing the formulation, given your knowledge. The UV absorbers in clear coats usually are designed to protect the substrate as well as themselves. Since these are already present, the only improvement you can make is to add pigments like carbon black. Even adding pigments can cause problems if you don't know what you are doing, and you do not do testing to confirm compatibility and performance. Ask coating suppliers for their recommendations.

RE: UV protection in thin layer PU coating

(OP)
CompositePro, thanks for your reply. There's nothing in the coating from the supplier's side. The HALS (and anti microbial)are added by us and I also need to find my own solution for protection of the substrate. The resin supplier suggests to talk to the additive suppliers and they generally favour their own solutions (TiO2 supplier is not selling UV absorbers).

I am hoping that someone has an unbiased opinion about what will work better for a thin coating.

I will eventually do a xenon test to evaluate the protection but they take time and cost money so I would like to take the right direction in first attempt.

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