Stabilization of electron beam curable compositions for improved exterior durability

A 100% solids coating composition polymerizable by low dosage ionizing radiation adapted to coat flexible substrates, which exclusive of pigments, initiators and other non-reactive components, consists essentially of an oligomer/monomer mixture of:

• (A) between about 90 and about 10 weight percent oligomer having the formula:
• ##STR14## wherein R' is hydrogen or methyl;
• and
• Y is a divalent urethane residue;
• and said oligomer has between about 0.5 and about 5 vinyl unsaturation units per 1000 units molecular weight of said oligomer;
• and
• (B) between about 10 and about 90 weight percent vinyl monomers polymerizable with said oligomer upon exposure to radiation, said vinyl monomers consisting essentially of (i) acrylic ester monomers and (ii) N-vinyl-2-pyrrolidone, wherein said N-vinyl-2-pyrrolidone is included in an amount of between about 3 and about 20 weight percent based on the total weight of (A) and (B), and
• (C) about 0.5 to about 5.0 parts each per 100 parts of the total of said organic resin and said monomer of:
• (i) benzotriazole selected from the group consisting of compounds having the formula:
• ##STR15## where R.sub.1 or R.sub.2 =H or an alkyl group of C.sub.1 -C.sub.25 ;
• and (ii) hindered amine selected from the group consisting of amines having the formula:
• ##STR16## wherein R=H or methyl.

A method for coating a substrate, the coating composition polymerizable by low dosage ionizing radiation, which comprises:

• (A) applying a first coating composition comprising up to about 60 weight percent pigment to the surface of a prepared substrate;
• (B) curing said first coating composition by exposure to an electron beam until an adherent dry coating is formed;
• (C) applying a second coating composition comprising 0-10 weight percent pigment to the coated surface of said substrate;
• and
• (D) curing said second coating composition by exposure to an electron beam until an adherent dry coating is formed;
• wherein said first coating composition and said second coating composition comprises an organic resin/monomer mixture of:
• (A) between about 97 and about 3 weight percent alpha-beta olefinically unsaturated organic resin containing between about 0.5 and about 5 vinyl unsaturation units per 1000 units molecular weight of said resin;
• and
• (B) between about 3 and about 97 weight percent vinyl monomers polymerizable with said resin upon exposure to radiation, said vinyl monomers comprising N-vinyl-2-pyrrolidone which is included in said composition in an amount of between about 3 and about 20 weight percent based on the total weight of (A) and (B);
• and
• (C) about 0.5 to about 5.0 parts each per 100 parts of the total of said organic resin and said monomer of:
• (i) benzotriazole selected from the group consisting of compounds having the formula:
• ##STR17## where R.sub.1 or R.sub.2 =H or an alkyl group of C.sub.1 -C.sub.25 ;
• and (ii) hindered amine selected from the group consisting of amines having the formula:
• ##STR18## wherein R=H or methyl.