Method for applying an organic coating onto an inorganic coated steel sheet

A substantially pollution-free method for uniformally improving the surface resistivity of oriented steel strip having an inorganic material as a surface insulating coating to produce an oriented steel strip-inorganic coating-organic resin composite capable of providing an average Franklin test reading of from 0.1 to 0 amperes at a pressure of up to 300 psi, which comprises,

• (1) treating the oriented steel strip with a UV curable solventless epoxy organic resin to a thickness of up to 0.2 mil, and
• (2) passing the treated oriented steel strip through an irradiation curing zone at a rate of up to 600 feet per minute, using an irradiation flux sufficient to effect the cure of the solventless epoxy organic resin to an organic resin hardness capable of being tested by the above-described Franklin test,
• where said UV curable epoxy organic resin is characterized by having a viscosity of up to 3,000 centipoises at 25.degree. C., and is a mixture comprising by weight
• (A) from 30 to 99% of a cycloaliphatic epoxy compound,
• (B) from 1 to 70% by weight of an oxirane containing organic material substantially free of cycloaliphatic radicals having a viscosity of less than 3,000 centipoises at 50.degree. C. and a molecular weight of less than 1,000, and
• (C) from 0.5 to 5% by weight of an onium salt,
• where the sum of (A), (B) and (C) is 100%, and said onium salt has the formula,
• [Y] .sub.j.sup.+ [MD.sub.k ] .sup.-.sup.(k.sup.-n)
• where M is a metal or metalloid, and D is a halogen radical, Y is a cation selected from the class consisting of
• [(R).sub.a (R.sup.1).sub.b Q] .sup.+ [(R).sub.c (R.sup.2).sub.d (R.sup.3).sub.e X] .sup.+ [(R).sub.f (R.sup.4).sub.g (R.sup.5).sub.h X] .sup.+
• where R is a monovalent aromatic organic radical, R.sup.1 is a divalent aromatic organic radical, R.sup.2 is a monovalent organic aliphatic radical selected from alkyl, cycloalkyl and substituted alkyl, R.sup.3 is a polyvalent organic radical forming a heterocyclic or fused ring structure selected from aliphatic radicals and aromatic radicals, R.sup.4 is a monovalent organic aliphatic radical selected from alkyl, alkoxy, cycloalkyl and substituted derivatives thereof, R.sup.5 is a polyvalent organic radical forming an aromatic heterocyclic or fused ring structure with Z, Q is a halogen radical, X is a Group VIa element selected from sulfur, selenium and tellurium, Z is a Group Va element selected from N, P, As, Sb and Bi, a is a whole number equal to 0 or 2, b is a whole number equal to 0 or 1, the sum of a+ b is equal to 2 or the valence of Q, c is a whole number equal to 0 or 3, d is a whole number equal to 0 to 2 inclusive, e is a whole number equal to 0 or 1, where the sum of c+ d+ e is a value equal to 3 or the valence of X, f is a whole number equal to 0 to 4 inclusive, g is a whole number equal to 0 to 2 inclusive, and h is a whole number equal to 0 to 2 inclusive and the sum of f+ g+ h is a value equal to 4 or the valence of Z,
• j= k- n
• n= valence of M and is an integer equal to 2 to 7 inclusive, and
• k is >n and is an integer having a value up to 8,
• where said irradiation curable solventless epoxy organic resin is capable of providing with 10C hydrocarbon oil, an interfacial tension reading of from 30-49/cm in accordance with ASTM D971-50 (1970).