PROCESS OF OBTAINING A POLYURETHANE COATING COMPOSITION HAVING EXTENDED POT-LIFE
The invention relates to polyurethane coating compositions having a pot-life of at least 8 hours and a de-blocking temperature of 50-100° C. The composition comprises: a) a blocked isocyanate formed by mixing at least one isocyanate functional compound with at least one imidazole and b) at least one polyol. The composition can be used on heat sensitive substrates. Methods of making such a composition are also described. The invention was applications in the coating industry.
1 . A process of manufacturing a polyurethane coating composition, said process comprising:
a) forming at least one blocked isocyanate wherein at least 75% of reactive isocyanate groups are blocked by mixing at least one isocyanate functional compound with at least one imidazole selected from the group consisting of a 2-monoalkyl substituted imidazole, a 4-monoalkyl substituted imidazole, a 5-monoalkyl substituted imidazole, a 2,4-dialkyl substituted imidazole, a 4,5-dialkyl substituted imidazole and a 2,4,5-trialkyl substituted imidazole, and
b) mixing said at least one blocked isocyanate with at least one polyhydric compound,
wherein the coating composition has a pot-life of at least 8 hours and a de-blocking temperature of 50-100° C.
2 . The process according to claim 1 , wherein said alkyl is a C 1 -C 10 linear or branched alkyl or cycloalkyl.
3 . The process according to claim 1 , wherein said imidazole is 2-ethylimidazole, 4-methylimidazole, 2-ethylimidazole, 2-propylimidazole, 2-isopropylimidazole, 2-ethyl-4-methylimidazole, or 4-methyl-5-hydroxymethylimidazole.
4 . The process according to claim 1 , wherein said aliphatic isocyanate functional compound is an isocyanate monomer, an isocyanate oligoconensate obtained from one pr more isocyanate monomers, or a mixtures of at least one said oligocondensate and at least one said monomer.
5 . The process according to claim 4 , wherein said oligocondensate is a biuret, a dimer, a trimer, an isocyanurate, a carbamate, an uretidinedione or an allophanate.
6 . The process according to claim 4 , wherein said oligocondensate comprises isocyanuric rings obtained from three isocyanate functional groups.
7 . The process according to claim 4 , wherein said isocyanate is tetramethylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, norbonane diisocyanate, 1,3-bis(isocyanatemethyl)cyclohexane, cyclohexane-1,4-diisocyanate, tetrahydrofuran diisocyanate, or a oligocondensate obtained from one or more of said diisocyanates.
8 . The process according to claim 5 , wherein said isocyanate is tetramethylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, norbonane diisocyanate, 1,3-bis(isocyanatemethyl)cyclohexane, cyclohexane-1,4-diisocyanate, tetrahydrofuran diisocyanate, or a oligocondensate obtained from one or more of said diisocyanates.
9 . The process according to claim 1 , wherein said polyhydric compound is a hydroxyfunctional polyacrylate or a hydroxyfunctional polyester having a molecular weight Mw of 3,000-50,000 g/mole.
10 . The process according to claim 1 , wherein said coating composition further comprises at least one pigment, surface active agent, organic solvent, catalyst and/or dehydrating agent.
11 . A method of obtaining a coated substrate, said method comprising applying a coat of the polyurethane coating composition according to claim 1 onto a substrate and subsequently stoving obtained coated substrate at 50-100° C.
12 . The method according to claim 11 , wherein said coated substrate is stoved at said temperature during 30-120 minutes.
13 . The method according to claim 11 , wherein said substrate is wood, plastic or paper.
14 . A polyurethane coating composition obtained by the process according to claim 1 , said composition comprising
a) at least one isocyanate functional compound, wherein at least 75% of reactive isocyanate groups are blocked with at least one imidazole selected from the group consisting of a 2-monoalkyl substituted imidazole, a 4-monoalkyl substituted imidazole, a 5-monoalkyl substituted imidazole, a 2,4-dialkyl substituted imidazole, a 4,5-dialkyl substituted imidazole and a 2,4,5-trialkyl substituted imidazole, and
b) at least one polyhydric compound,
wherein the coating composition is suitable for use on heat sensitive substrates and has a pot-life of at least 8 hours and a de-blocking temperature of 50-100° C.
15 . The composition according to claim 14 , wherein said alkyl is C 1 -C 10 linear or branched alkyl or cycloalkyl.
16 . The composition according to claim 14 , further comprising at least one pigment, surface active agent, organic solvent, catalyst and/or dehydrating agent.
17 . A polyurethane coating composition comprising
a) at least one isocyanate functional compound, wherein at least 75% of reactive isocyanate groups are blocked with at least one imidazole selected from the group consisting of a 2-monoalkyl substituted imidazole, a 4-monoalkyl substituted imidazole, a 5-monoalkyl substituted imidazole, a 2,4-dialkyl substituted imidazole, a 4,5-dialkyl substituted imidazole and a 2,4,5-trialkyl substituted imidazole, and
b) at least one polyhydric compound.
wherein the coating composition is suitable for use on heat sensitive substrates and has a pot-life of at least 8 hours and a de-blocking temperature of 50-100° C.
18 . The composition according to claim 17 , wherein said alkyl is C 1 -C 10 linear or branched alkyl or cycloalkyl.
19 . The composition according to claim 17 , further comprising at least one pigment, surface active agent, organic solvent, catalyst and/or dehydrating agent.