Moisture and heat resistance of film

For painted products used in humid tropical regions, the damp heat test is also a method to evaluate the protective performance of the coating film. According to the provisions of GB/T1740-89, the painted test panel is hung vertically in a humid heat box. The experimental conditions are temperature 47°C±1°C and relative humidity 96%±2%. During the test, there must be no condensation on the surface of the test plate. Check once every 48 hours, and then every 72 hours. After each inspection, the position of the test plate should be changed until the end of the test within the specified time, and finally rated according to Table 3_8_3. When rating, the 150mmx70mmx (0.5~2)mm plexiglass plate is divided into one hundred equal parts, which is used to measure the foaming area.

Note: ① Calculation of the foaming area, using a 100% grid plate, as long as 1% of the area has foam, it is counted as 1% of the area, and so on.

Blistering grades are as follows: microbubbles, which are only visible to the naked eye; small bubbles, which are clearly visible to the naked eye, with a diameter of less than 0.5mm; medium bubbles, with a diameter of 0.6~1mm; large bubbles, which are more than 1.1mm in diameter.

② The surrounding edge of the test plate (including the edge sealing) and the 5mm around the hole are not assessed, and the damage caused by external factors is not calculated.

③If the paint film damage phenomenon meets any one of the grades specified in the above table, it belongs to the grade.

GB/T138-93, IS06270 and ASTMD4585-92 adopt continuous condensation method. The temperature of the Water Bath is 42°C ± 2°C, and the air temperature in the 25mm space below the test plate is 37°C ± 2°C, so that the coating surface is continuously in a condensed state, which is conducive to water penetration. Humidity test equipment has been developed to a combined cycle test of immersion, drying, and damp heat.