Study on the Method of Predicting Service Life of Coated Steel Sheets (IV)

Predicting the Service Life for Peeling off of Polyvinyl Chloride Resin Coated Galvanized Steel Sheet

Abstract

For applications of polyvinyl chloride resin coated galvanized steel sheet to outdoor building materials, the coated film sometimes peels off depending on the use conditions. Therefore, a need has existed for developing method for predicting the life time of the coated steel sheet for peeling off.
This paper examines the service life for peeling off of the coating film of polyvinyl chloride resin coated galvanized steel sheet, by measuring the amount of the chlorine in the surface layer of polyvinyl chloride resin coating film with fluorescent X-rays to obtain the degree of the decomposition of polyvinyl chloride resin.
The results obtained are as follows;
(1) The amount of the chlorine in polyvinyl chloride resin can precisely be measured with the intensity ratio of ClKα/TiKα of fluorescent X-rays.
(2) There is a correlationship between peeling off and retention rate of ClKα/TiKα in outdoor weathering test. When the retention rate gets under 70%, the condition for the peeling off of coating film suffices.
(3) The successive change of ClKα/TiKα retention rate in outdoor weathering test is affected by the film thickness of polyvinyl chloride resin, and the amounts of titanium dioxide pigment and iron oxide pigment.
(4) The service life for peeling off of the coating film of polyvinyl chloride resin coated galvanized steel sheet can be predicted in a short period by obtaining the successive change of the retention rate of ClKα/TiKα in accelerated weathering test.