As the temperature continues to rise, the gas accumulated in the vicinity of the buried hole is more and more, forming a large expansion pressure, so that the browning surface of L2 and the PP are subjected to a separation force for separating them.When the final expansion pressure (f) is less than the adsorption force (F) between the browning surface and the PP (fF), separation occurs between the browning surface of L2 and PP. A distinct blocky blistering phenomenon.