Pre-coated metal sheet surface treatment agent, coated ground-treated metal sheet coated with the same, and pre-coated metal sheet excellent in processing adhesion of coating film using the same

摘要

Disclosed is a surface treatment agent, with a pH from 2.0-6.5, for use on a pre-coated metal sheet. In water, the surface treatment agent contains as solids: polyester resin of which the particle diameter ranges from 50-150nm, the glass transition temperature (Tg) is from 0-30°C and the hydroxyl number is from 5-13; tannins or tannic acid; a silane coupling agent; and silica particulate. The disclosed surface treatment agent, which does not generate deposits during the lengthy stationary state during the actual production of a pre-coated metal sheet, is a stable surface treatment agent for use on a pre-coated metal sheet.