Hardening Behavior of Polyester/ Iso-cyanate Resin Paint Film Heated on Steel Sheet and their Influence on Bubble Defect (Popping)

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By using polyester/ iso-cyanate resin solutions as model paints, the relation between the hardening behavior of the paint film heated on the steel sheet and the maximum film thickness without bubble defect (the popping) occurring was examined by using the TBA (Torsional Braid Analysis) method. The results were as follows.1)In the cure process of the paint film, two dimensional crosslinking reactions are firstly begun, and subsequently, three dimensional crosslinking reactions are begun. The evaporation of volatile elements such as solvents did not receive a big influence from the two dimensional crosslinking reactions, and was started being obstructed after the three-dimensional crosslinking reactions were begun.2)In the comparison of the resin solutions, the lower the starting temperature of the three-dimensional crosslinking reaction (T3) was, the more easily the popping occurred. The more the numbers of functional groups of resin were, the lower the T3 value was. Furthermore, when the number of functional groups were same, the higher the Tg value of the resin was, the lower the T3 value was.