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

Part30. Discussion on etching process before chromium-free chemical conversion 6

Abstract

In this paper, effect of aluminum alloy surface etching process before chromium-free chemical conversion on durability of polyester powder coating is discussed based on outdoor exposure tests for three years at Southwest islands in South of 28 degrees north latitude. Main results are as follows. (1) At Ikeijima and Miyakojima islands Okinawa prefecture, all specimens of HAA hardening type poly ester powder coating have remarkable blisters around the X-cut part. On the other hand, slight blisters are observed at Yabuchijima Okinawa and Okinoerabu Kagoshima test sites. And gloss down of the coating surface differs with outdoor exposure sites and coating hardening type. These differences of the coating deterioration match our past reports. (2) At Ikeijima and Yabuchijima, distinguished blisters are observed at the edge of the HAA hardening type specimen. Therefore, the acid-etching process before the chromium-free chemical conversion is useful to durability improvement of the coating. (3)Isocyanate hardening type coating is lesser blistering than the HAA type. (4)The coating film weatherability evaluation would be able to be judged with 24-month-term-outdoor exposure tests at Southwest islands in South of 28 degrees north as well as our research of the past.