Blister box test

Blister Box Test, according to ASTM D 4585 (ISO 6270). This test evaluates the water resistance of a coat by condensation of water vapour. The panel surface with the coating system is exposed to 40°C, saturated water vapour, at an angle of 15° to the horizontal. The reverse side of the panel is exposed to room temperature. At each inspection blisters and rust are evaluated according to ASTM D 714 (ISO 4628-2) and ASTM D 610 (ISO 4628-3) respectively. Cracking is evaluated according to ISO 4628-4. When the test is stopped, adhesion is evaluated according to ASTM D 3359, tape test (ISO 2409) or ASTM D 4541 (ISO 4624), pull-off test. 

Fog Boxes vs. Rain. Like many other accelerated tests, the fog box blister-resistance test shows trends rather than an exact correlation with the results observed in actual rainfall. When deionized water is used for the spray in the fog box, the test is most stringent, and blister differences can be observed in paints that do not blister when the much less stringent tap water fog is used. The tap water test correlates more closely to what is generally seen on the test fences when paint films no more than a few days old are exposed to rain. 

Zinc Oxide. We found that as little as 5 lb of zinc oxide per 100 gal (1 gal = 3.785 L) of paint was sufiBcient to impart acceptable early blister resistance to the paint when tested in the rain or in the tap water fog box (Table I). Higher zinc oxide levels showed no further blister-resistance improvement in this paint. Blistering in the deionized water fog box was so severe that even the HEC-thickened control had a blister rating of 4D. (The note to Table I explains the rating method used.) However, a noticeable effect occurred at zinc oxide levels of 5 lb/100 gal of paint and higher. The zinc oxide combined with the ammonia in the paint and formed a zinc ammonium complex that may ionically cross-link the carboxyl groups in the HASE thickener and other paint constituents, and thereby reduce the overall water sensitivity of the paint. 

Zinc Ammonium Complexes. The zinc ammonium complexes were tested on a different chalky latex panel than the zinc oxide paints, and the entire series showed less blistering in the same deionized water fog box (Table II). The HEC-thickened control did not blister on this board. The HEUR control showed 7M blisters on this board vs. 2MD (Table I). Addition of the zinc ammonium complexes resulted in much-improved early blister resistance. Blister-resistance effectiveness differed depending on which complex was used. The four zinc ammonium complexes evaluated in the HASE-... 

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