Polyisocyanate-based anti-corrosion coating
Anti-corrosion coating for metallic substrates obtainable by reacting an organic polyisocyanate with a compound containing isocyanate-reactive hydrogen atoms at an isocyanate index of between 1000 and 5000% in the presence of a trimerisation catalyst.
1. A polyisocyante based non-syntactic primer coating composition comprising the reaction product of (i) an organic polyisocyanate and (ii) a compound containing isocyanate-reactive hydrogen atoms wherein components (i) and (ii) are reacted at an isocyanate index from about 2400 to 10000% in the presence of a trimerisation catalyst; wherein the organic polyisocyanate is a semi-prepolymer or a prepolymer that is obtained by reacting (a) a polyisocyanate compound with (b) a compound containing isocyanate-reactive hydrogen atoms; and wherein component (ii) and component (b) may be the same or different and are selected from the group consisting of alcohols, glycols, polyether polyols, polyester polyols, mercaptans, amines, urea, and amides.
2. The primer coating composition according to claim 1 , wherein the isocyanate content of component (i) is between 6 and 30 wt %.
3. The primer coating composition according to claim 1 , wherein the functionality of component (i) is from 2.0 to 2.9.
4. The primer coating composition according to claim 1 , wherein component (ii) is hydrophobic.
5. The primer coating composition according to claim 4 , wherein component (ii) is a polyether polyol obtained by ring-opening polymerisation of propylene oxide with isocyanate-reactive initiators of functionality 2 to 8 and/or a polyester polyol obtained by reacting a polyhydric alcohol and dimer acid.
6. The primer coating composition according to claim 1 , wherein the weight ratio between component (i) and component (ii) is between 1/1 and 10/1.
7. The primer coating composition according to claim 1 , wherein the isocyanate index is between 2400 and 5000%.
8. The primer coating composition according to claim 1 , wherein the isocyanate index is between 2400 and 4000%.
9. The primer coating composition according to claim 1 , wherein the isocyanate index is about 2400%.
10. The primer coating composition according to claim 1 , wherein the isocyanate content of component (i) is between 10 and 26 wt %.
11. The primer coating composition according to claim 1 , wherein the isocyanate content of component (i) is between 16 and 20 wt %.
12. The primer coating composition according to claim 1 , wherein the functionality of component (i) is from 2.2 to 2.5.
13. The primer coating composition according to claim 1 , wherein the weight ratio between component (i) and component (ii) is between 1/1 and 4/1.
14. An article comprising a substrate and a film coating adhered thereon wherein the film coating comprises the primer coating composition as defined in claim 1 .
15. A process for inhibiting corrosion of metallic surfaces comprising applying to the metal surface the reaction mixture of claim 1 and curing it at a temperature of at least 60° C.
16. The process according to claim 15 , wherein the curing step is conducted at a temperature of at least 80° C.
17. The process according to claim 15 , wherein the curing step is conducted at a temperature of at least 100° C.