Conductive primer composition

Claim 1

A primer composition comprising solvents and about 40-75% by weight of a film forming binder and pigments in a pigment to binder ratio of about 5:100-50:100; wherein the pigments comprise an electrically conductive non-surface treated carbon black pigment and the binder consists essentially of about (1) 40-70% by weight, based on the weight of the binder, of a polyester copolymer having linear segment with hydroxyl groups consisting essentially of the esterification product of a straight chain diol having 2-10 carbon atoms and an aliphatic dicarboxylic acid or an aromatic dicarboxylic acid or a mixture of said dicarboxylic acids, said linear segment having a hydroxyl number of about 15-300 and a number average molecular weight of about 300-3,000 and branched segments having hydroxyl groups consisting essentially of the esterification product of a straight chain diol having 2-10 carbon atoms, a branched chain polyol and an aliphatic dicarboxylic acid or an aromatic dicarboxylic acid or mixture of said dicarboxylic acids said branched segments having a hydroxyl number of about 175-300 and number average molecular weight of about 500-2000 and being attached to linear segment by esterification of hydroxyl groups with a diacid or an anhydride wherein molar ratio of linear segment/diacid or anhydride/branched segment is about 1/1/1; (2) 30-60% by weight of an alkylated melamine formaldehyde crosslinking agent consisting essentially of a blend of a methylated melamine formaldehyde resin having alkoxy imino groups and a methylated melamine formaldehyde resin; wherein the composition forms a hard flexible electrically conductive coating on a plastic substrate whereby the coated plastic substrate can be bent 180° around a 1/2 inch mandrel with the coating facing outward and the coating exhibits substantially no breaks or cracks when tested at -18° C. and the coating has a surface conductivity of at least 160 Randsburg units.