Environmental management for baked enamel coating system onto aluminum alloy building materials

Part28　Discussion on etching process before chromium-free chemical conversion 5

Abstract

Chromium-free chemical conversion and powder coating for aluminum alloy building materials have been continuously studied. This paper discribes the influence of etching process before the chromium-free chemical conversion in polyester powder coating and difference of the coating film deterioration between outdoor exposure test sites. Main results are as below. (1)Deterioration of the HAA hardening type polyester powder coating film differs markedly with the test sites. This is in agreement with the previous reports. (2)It is judged that durabity of the powder coating is affected by the etching process before the chemical conversion and the selection of the conversion chemical agents. (3)The blistering of all specimens of the isocyanate haradening type polyester powder coating film is more slightly observed than the HAA type ployester. (4)The film blistering on some of the exposed specimen is extended in the term extending from 12-month-exposed until 24-month in all test sites. On the other hand, many specimen has no blistering or no change of the blistering. Therefore, the outdoor exposure test in South of 28th parallel north of Nansei-shoto (southwestern islands off Kyushu and in the Okinawan archipelago) is useful for the coating durabilty evaluation.