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

Influence of sunshine weatherometer testing temperature 2on coating film deterioration

Abstract

Black panel temperatures were held higher than the standard in sunshine weatherometer testing, and the properties of coating film as deteriorated on thermosetting or thermoplastic resin coated steel sheets were examined in view of appearance change and chemical changes in coating resin. As a result :
(1) Coating resin as found on polyester resin coated steel sheets deteriorates in photo-oxidation mode because of alternate effects of Uv × Hu and Te × Hu, and the following rate equation holds.
In r=-20,000/RT 30. 44
With testing temperature rise, the deterioration condition differs from that in outdoor weathering testing.
(2) Coating resin as found on silicone polyester resin coated steel sheets deteriorates in photothermal reaction mode because of an alternate effect of Te × Hu, and the following rate equation holds.
In r=-30,000/RT+ 44. 45
The deterioration condition, however, differs depending on the testing temperature.
(3) Coating resin as found on polyvinyl chloride resin coated steel sheets deteriorates in photooxidation mode because not so much of Te as of Uv or Hu, and the following rate reaction holds.
In r=-15,000/RT+22. 00
The condition of a coating film deteriorated is hardly influenced by testing temperature at all, however, film cracking is apt to occur with temperature rise.
Note : r : acceleration ratio
R : gas constant
T : testing temperature (°K)
Uv : quantity of integrated ultraviolet rays
Hu : integrated time of maximum humidity
Te : integrated time of maximum temperature