For flexible plastics, coatings must not only protect the plastic substrate, but also be just as elastic. With their tunable flexibility, polyurethanes are an ideal solution.
Most polyurethanes are reactive systems that require curing with the use of a hardener or crosslinker. Yet, some plastics are sensitive to the reactive curing process. For sensitive substrates, it is preferable to use a non-functional or non-reactive flexible polyurethane system that cures via a physical drying process.
Desmolac® non-functional linear polyurethanes from Covestro are designed for the formulation of flexible, physically drying solventborne primers and topcoats for plastics.
The hardness of these coatings is due to interactions between the polymer molecules, rather than through the formation of a crosslinked network. They are very flexible as a result.
The addition of a polyisocyanate that can undergo a mild crosslinking reaction with moisture in the air once the coating is applied is an effective way to increase the solvent resistance of coatings based on physically drying Desmolac® binders. Desmodur® N 75 (10-20% based on solid resin) is a recommended grade for this purpose.
Desmolac® non-functional resins are also used as co-resins in coatings applied to other flexible substrates.
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