Example 7
The polyamide-imide film having a thickness of 50 μm was subjected to repeated folding to have a radius of curvature of 1 mm and then unfolded (the number of folding counts one upon folding and unfolding). If it was not fractured upon repeated folding of 200,000 times, it was indicated as Pass. If fractured before repeated folding of 200,000 times, it was indicated as Fail. The number of folding times was counted using the U-shape folding equipment of YUASA.