Composite organic-coated steel sheet.

摘要

A composite organic-coated steel sheet suitable for use in automobile bodies comprises a steel sheet plated with zinc or a zinc alloy and having on the plated surface on one or both sides of the steel sheet a lower chromate film and an upper organic resin coating film. The upper organic coating film has a thickness of 0.1 - 5 mu m and is formed from a primer composition which comprises, in an organic solvent, (1) 100 parts by weight of an epoxy resin having a number-average molecular weight of from 500 to 10,000, (2) from 10 to 60 parts by weight of an aromatic polyamine containing from 2% to 30% by weight, based on the aromatic polyamine, of a promoter selected from the group consisting of phenol compounds and cresol compounds, (3) from 10 to 60 parts by weight of a polyisocyanate, and (4) from 10 to 40 phr of silica particles of colloidal silica or fumed silica or a mixture of these.