Process for applying a coating to coiled metal sheet
The invention relates to a process for preparing a coated metal sheet coil comprising the coating of the metal sheet with a curable composition comprising an (meth)acrylated oligomer which is the reaction product of a carboxyl functionalized polybutadiene comprising x equivalents of —COOH groups with (i) y equivalents of one or more (meth)acrylated monoepoxides or (ii) a mixture of z equivalents of one or more polyepoxides and at least (z-x) equivalents of an α,β-unsaturated carboxylic acid; with z>x and y≧x.
1. Process for preparing a coated metal sheet coil comprising the following steps:
(1) decoiling of the coiled metal sheet;
(2) coating the metal sheet with a curable composition comprising a/an (meth)acrylated oligomer which is the reaction product of a carboxyl functionalized polybutadiene comprising x equivalents of —COOH groups with a mixture of z equivalents of one or more polyepoxides and at least (z-x) equivalents of at least one α,β-unsaturated carboxylic acid with z>x;
(3) curing the composition by electron beam or UV-radiation; and
(4) recoiling the coated metal sheet.
2. Process according to claim 1 , wherein the carboxyl functionalized polybutadiene is the reaction product of a hydroxyl-terminated polybutadiene with a cyclic anhydride corresponding to the formula (I):
wherein R represents arylene, cycloalkylene, alkylene or alkenylene group, optionally substituted by an alkyl group, an alkenyl group, a —COOH group and/or another anhydride group.
3. Process according to claim 2 , wherein the cyclic anhydride corresponding to formula (I) is phthalic anhydride or dodecenylsuccinic anhydride.
4. Process according to claim 1 , wherein z is greater than 2x.
5. Process according to claim 1 , wherein α,β-unsaturated carboxylic acid is chosen from acrylic and methacrylic acid.
6. Process according to claim 1 , wherein the polyepoxide is chosen from diglycidylethers of aromatic or aliphatic diols or cycloaliphatic diepoxides.
7. Process according to claim 6 , wherein the polyepoxide is chosen from diglycidyl ether of bisphenol-A, diglycidylether of poly(ethylene oxide-co-propylene oxide), diglycidylether of polypropylene oxide and diglycidylether of butanediol.
8. Process according to claim 1 , wherein the (meth)acrylated oligomer is prepared by adding the α,β-unsaturated carboxylic acid to the carboxyl functionalized polybutadiene before or at the latest at the same time as the polyepoxide.
9. Process according to claim 1 , wherein the (meth)acrylated oligomer is obtained by the reaction of the carboxyl functionalized polybutadiene and the polyepoxide in the presence of at least one non reactive diluent chosen from mono- or polyfunctional (meth)acrylate monomers.
10. Process according to claim 9 , wherein the non reactive diluent is chosen from phenoxyethyl acrylate, isobornyl acrylate, n-butyl acryloyloxy ethyl carbamate and their mixtures.
11. Process according to claim 1 , wherein the curable composition comprises:
from 8% to 50% by weight of said (meth)acrylated oligomer,
from 0 to 65% by weight of non-reactive diluent,
from 0 to 60% by weight of additional diluent chosen from copolymerizable ethylenically unsaturated monomers,
from 0.01 to 60% by weight of (meth)acrylated polyepoxide,
from 0.01 to 5% by weight of photoinitiator or chemical initiator, and
from 0 to 20% by weight of adhesion promoter.