Polyurethane resins and varnishes
How two-component polyurethane varnishes harden?
Two-component polyurethane varnishes harden by polyaddition, the hardener polyisocyanate is bonded to the main paint component.
Please describe the curing of the two-component polyurethane varnish
The main component of polyurethane varnish consists of saturated polyesters or polyethers with hydroxyl groups (OH). The hardener contains polyisocyanate. After mixing the main component with the hardener, the polyisocyanate reacts with the hydroxyl groups of the main component, wherein the hydrogen of the OH group swaps with the nitrogen of the isocyanate group. This allows the polyisocyanate to be chemically bonded to the main paint component. It is a polyaddition process.
What main solvents are included in special thinners for polyurethane varnishes?
Special thinners for polyurethane varnishes mainly contain ketones and esters.
Please describe the different options for curing polyurethane varnishes, Hardening under the influence of moisture Polyurethane varnishes, hardening under the influence of moisture, they are single-component. Depends on the composition of the paint, there are two ways to harden it:
1. Poliizocyjanian jest już zmieszany z poliestrem łub polieterem, however, blocking agents do not allow the chemical reaction. After applying the varnish to the substrate, the blocking agent reacts with the moisture in the air. As a result, polyaddition takes place with the participation of polyisocyanate and hydroxyl groups of polyester or polyether, and consequently – hardening of the varnish.
2. Druga możliwość utwardzania lakieru także wymaga zastosowania poliizocyjanianu. Here, however, polyesters or polyethers with a lower number of hydroxyl groups are used. After applying the varnish to the substrate, the polyisocyanate reacts with the moisture in the air, forming polyamines, which in turn react with another polyisocyanate, forming polyurea. This polyaddition causes the lacquer to harden.
Please list the fields of application for polyurethane varnishes and paints
Polyurethane varnishes and paints are used to make coatings subject to high mechanical and / or chemical loads on all substrates. A special field of application is corrosion protection. For this purpose, polyurethane resin topcoats with an epoxy resin backing are used. Polyurethane varnishes, hardening under the influence of moisture, are readily used to protect parquet.