PRIMARY RUST PREVENTIVE COATING COMPOSITION AND USE THEREOF

摘要

Provided is a primary rust-preventive coating composition which by being dried and cured at room temperature is capable of forming a coating film having an average dry film thickness of not more than 10 µm even with the use of conventional coating machines and which has excellent rust prevention properties and overcoatability as well as excellent weldability/cut-ability at the time of welding and cutting steel plates. The primary rust-preventive coating composition includes a siloxane-based binder (A) having a weight average molecular weight (Mw) as measured by gel permeation chromatography (GPC) in terms of standard polystyrene being 1000 to 6000 and a zinc dust (B) including a flaky zinc-based powder (b-1), the primary rust-preventive coating composition having a pigment volume concentration (PVC) of 35 to 60%, and having a mass ratio ((B)/(A)) of the zinc dust (B) to the siloxane-based binder (A) in terms of SiO 2 being 1.0 to 5.0.